Polymers wastes create great environmental problems in different ways and therefore should be properly disposed. To convert these waste polymers to other useful products like feedstock chemicals and fuel is a promising solution to these problems. The objective of this work is to develop environmental friendly methods for the degradation of Highdensity polyethylene (HDPE) into useful products which could be directly or indirectly used as chemicals or fuel. The first chapter of this dissertation is concerned about a brief introduction of different types of polymers. It includes history and classification of polymers and information regarding the types, formulas, structures and characteristic of different types of polymers. Different types of polyethylenes have been discussed in this chapter. It focuses specifically on HDPE and its different preparation methods have been included in this chapter. It also describes properties and applications of polyethylene (PE), more specifically HDPE. Several degradation methods and mechanistic aspects of the degradation processes have been discussed. The second chapter covers a thorough review of the recent and relevant literature reported for the thermal and thermocatalytic degradation of PE and HDPE. Chapter III consists of experimental methods applied for thermal and catalytic conversion of HDPE. Different equipments used in the study and experimental procedures have been discussed. Indigenous batch reactor and furnace consisting of IR heating elements were used for the catalytic and thermal pyrolysis of HDPE. The liquid products were fractionated and the fractions were analyzed by GC and GC/MS. Different physical parameters for the oil products were studied. Chapter IV is concerned with results and discussion about the experimental findings. For maximum conversion into oil products, conditions like temperature, catalyst weight and reaction time and nitrogen flow rate were optimized. Several catalysts like MgCO3, CaCO3, BaCO3, Ultra stable Y-zeolite (US-Y), were applied for the catalytic degradation of HDPE. Different temperatures like 250oC, 300oC, 350oC, 395oC, 400oC, 410oC, 420oC, 430oC, 440oC, 450oC, 460oC and 480oC were explored in order to find out the optimum reaction temperature for thermal and catalytic degradation process of HDPE. From the catalytic degradation of HDPE using these catalysts, it was found that among the carbonates, MgCO3 and CaCO3 were approximately effective up to an equal extent in terms of total conversion (96.80% and 97.20% respectively) and oil yield (51.87% and 52.33% respectively) but the temperature for the later catalyst was 460°C and for the former it was 450°C. Reaction time and cat/pol ratio in both the cases were same (1.5 h). In case of BaCO3 catalyst the total conversion (96.07%) was comparable with total conversion achieved with MgCO3 and CaCO3 but the liquid yield (41.33%) was considerably low. Among the applied zeolite catalysts, the powdered US-Y was found to be the most efficient catalyst for the degradation of HDPE. With US-Y catalyst, a total percent conversion of 96.70% was achieved in a 25min experiment with nitrogen flow rate of 10mL/min and a cat/pol ratio of 1:8 at a very low reaction temperature of 395°C. The % oil yield in this case was 71.45%. Under the same experimental conditions but at a higher temperature (420°C), the total % conversion achieved was 96.34% with a little increase in the % oil yield (72.13%). The liquid products obtained thermally and catalytically in bulk quantities were fractionated at different temperatures like100°C, 150°C, 200°C, 250°C and 300°C. The parent liquid products and the fractions collected at different temperatures were characterized by physicochemical tests. The physical parameters like refractive index, density, specific gravity, API gravity, viscosity, kinematic viscosity, flash point, calorific value and ASTM distillation were determined according to IP and ASTM standard methods for fuel values. From the physical tests, it was observed that the results for the liquid fractions were somehow comparable with the standard values for gasoline, kerosene and diesel oil. All the fractions and parent liquids were analyzed by GC and on the basis of boiling point distribution (BPD), the composition of samples was investigated. GC/MS analysis of these samples was also conducted in order to determine the exact composition of thermally and catalytically derived liquids. With increasing distillation temperature, a gradual increase in the percentage of heavier hydrocarbons was observed. It could be concluded, that catalytic degradation of HDPE yields valuable products in terms of fuel oils and chemical feedstocks on one hand and could be a best solution to environmental problems caused by HDPE on the other hand. However more efforts are required to apply this catalytic degradation process for the proper disposal of waste HDPE on industrial scale.