Low cost and eco-friendly activated carbon (AC) was prepared from a cheap precursor material, used tea leaves (UTLs), by chemical activation with phosphoric acid (PA) under optimum conditions, using central composite design (CCD) of response surface methodology (RSM). The conditions optimized were activation temperature, chemical impregnation ratio (IR) and activation time with % age yield, iodine (I2) and methylene blue (MB) number as the targeted responses. The optimal preparation conditions were determined as: activation temperature of 600 oC, impregnation ratio (IR) of 1.30 and activation time of 130 min, under which a carbon yield of 33.55 % and I2 and MB uptake of 1051 mg g-1 and 321 mg g-1 respectively, could be achieved. The AC produced by phosphoric acid activation under optimal conditions (PA-AC) was subsequently modified with hydrogen peroxide and anionic surfactant, sodium dodecyl sulfate (SDS). The optimal (PA-AC), hydrogen peroxide (PA-AC-HO) and SDS modified carbons (PA-AC-SDS) were utilized for cationic dyes removal from aqueous medium.PA-AC, PA-AC-HO and PA-AC-SDS were characterized by various physio-chemical techniques including TG/DTA, SEM, XRD, FTIR spectroscopy, BET surface area, Boehm’s titration, pHPZC and proximate-ultimate analysis. Results showed that all the three adsorbents have sufficient number of acidic functional groups and their pHPZC values lies in the acidic region. The pHPZC values of PA-AC, PA-AC-HO and PA-AC-SDS were found to be 4.60, 3.40, and 5.20, respectively. Boehm’s titration results showed that PA-AC-HO surface has more acidic groups than PA-AC and PA-AC-SDS. TG/DTA analysis of the three samples showed very small weight loss in the temperature range 110-1000 oC indicating high carbon and low volatile matter content which is supported by EDX and proximate analysis results. XRD analysis showed the amorphous nature of the three samples.PA-AC has larger BET surface area and micropore volume than PA-AC-SDS and PA-AC-HO while, PA-AC-HO has greater fraction of mesopore volume (57.83 %). The SEM study confirmed that the external surface of raw UTLs is rough with few small pores while that of PA-AC, PA-AC-HO and PA-AC-SDS is highly porous with numerous cavities which make them suitable to adsorb cationic dyes from aqueous solutions. Pore widening and some cracks were also observed on PA-AC-HO surface with a corresponding BET surface area and micropore volume decrease. The SEM analysis also showed that after cationic dyes uptake most of the pores disappeared in all the three AC samples due to saturation with dyes molecules. xi To find the efficiency of the prepared adsorbents, all the three AC samples were utilized for the adsorption of five cationic dyes BB-9, BY-2, BB-41, BG-4 and BV-3 from aqueous mediums by studying different process parameters. The uptake of all these dyes by PA-AC, PA-AC-HO and PA-AC-SDS was low in the acidic pH range (pH 2.0-4.0) and increased with increasing pH of the solution beyond 4.0. Dyes uptake per unit mass of adsorbents was highly dependent on dyes initial concentrations, contact time, adsorbent dose, particle size and ionic strength. Kinetic data was analyzed using different models to explain the rate and mechanism of BB-9, BY-2, BB-41, BG-4 and BV-3 adsorption onto PA- AC, PA-AC-HO and PA-AC-SDS. The adsorption data was described by pseudo-second order kinetic model having high coefficients of correlation (R2 ˃ 0.99), and the qe calculated were in close agreement with the experimentally determined adsorption amount (qe, exp) for each cationic dye at all the studied concentrations. The rate constant k1 (min-1) values for PA-ACHO were higher than PA- AC and PA-AC-SDS. Intra-particle diffusion and Boyd’s models verified that during interaction of the dyes with PA-AC, PA-AC-HO and PA-AC-SDS both film diffusion and intra-particle diffusion may occur parallel. Langmuir and Temkin isotherms models explained the equilibrium adsorption data very well as evident from R2 values. The value of binding energy constant (KL) for all adsorbents were higher at high temperature, showed favorable adsorption of dyes at higher temperature. Moreover, the values of separation factor (RL) lies between 0 and 1, confirming that adsorption of BB-9, BY-2, BB-41, BG-4 and BV-3 onto PA-AC, PA-AC-HO and PA-AC-SDS can be described very well by Langmuir model. The positive ∆Ho values showed endothermic nature of BB-9, BY-2, BB-41, BG-4 and BV-3 adsorption onto PA-AC, PA-AC-HO and PA-AC-SDS. The positive ∆So values suggested increased randomness at solid/liquid interface during the adsorption process which reflects high affinity of these adsorbent for cationic dyes. The ∆Go values were negative at all the temperatures studied, suggesting spontaneous nature of dyes adsorption. In binary systems the individual dyes adsorption capacities [qe,i(mg g-1)] and adsorption yield [Adi,%] were smaller than those estimated for each dye in single component solution, showing antagonistic adsorption of dyes. Regeneration of dyes loaded adsorbents was carried out by five consecutive cycles. Results showed that PA-AC has good regeneration capacity, followed by PA-AC-SDS and PA-AC-HO. Subject Headings: Surface Chemistry, Material Chemistry, Environmental Chemistry, Advanced Instrumental Techniques, Statistical Optimaization Techniques, Chemical Kinetics, Thermodynamics, Ion Exchange, Dyes and Pigments, Environmental remediation