This dissertation; Synthesis and biological evaluation of 1,2,3-benzotriazin 4(3H)-one based compounds comprises easy preparation of new compounds and study of their enzyme inhibition assay. Three series of 1,2,3-benzotriazin-4(3H)-one sulfonamide / carboxamides were synthesized in good to excellent yields. For the preparation of first series isatin was converted to isatoic anhydride, then reacted with sulfanilic acid followed bydiazotization to cyclize to 4-(4-oxobenzo[d][1,2,3]triazin 4(3H)-yl)benzenesulfonic acid. The acid was directly converted to series of sulfonamides by using 1,3,5-trichlorotriazine:N,N-dimethylformamide (TCT: DMF) adduct at room temperature. The reaction was found successful only for electron rich anilines. For the second series, isatin was converted to of 4-(4 oxobenzo[d][1,2,3]triazin-3(4H)-yl)butanoic acid through isatoic anhydride. Then N (4-(1H-benzotriazol-1-yl)-4-oxobutyl)benzo[1,2,3]triazin-4(3H)-one was synthesized by reacting the acid with thionyl chloride and benzotriazole. Further at room temperature benzotriazole moiety was replaced with different amines and anilines to afford amide derivatives. In another series 6-amino-N-alkyl-1,2,3-benzotriazin-4(3H)-ones were used to prepare sulfonamide derivatives by reaction with different sulfonyl chlorides. All the prepared compounds were evaluated for their enzyme inhibition potency. α-Glucosidase, Urease and Acetylcholinesterase were used to study. Results indicated that most of the compounds have potential to inhibit α-glucosidase better as compared to standard drugs. Anti-urease results showed fair to good inhibition activity but less than refernce compound; thiourea. In case of acetylcholinesterase, none of the compound found active.