The present work was carried out to propose the use of processed waste plastic (P.E.T) and steel slag aggregate (SSA) for the modification of bituminous mix in order to cater the need of the enhancing the performance of flexible pavements as well as to minimize the quantum plastic waste in society as they have been posing a serious threat to environment. There are two methods available namely wet and dry process of incorporating waste plastics into bituminous mixes. Research work has been carried out by adopting the wet process. In this study, wet process is carried out on the grade1 suggested by MoRTH and IRC for BC mixes. The Marshall method of mix design was adopted using Penetration grade 60/70 binder to find the optimum binder content for all conventional as well as modified bituminous mixes and to find out optimum plastic and steel slag content that can replace these conventional materials. Marshall Specimens were prepared at bitumen contents of 4.0, 4.5, 5.0% by weight to find optimum bitumen content, with P.E.T content of 0%, 4%, 6%, 8%, 10% by weight of bitumen and with steel slag aggregate content of 5%, 10% and 15% to find out respective limits and their properties. Marshall Stability, Flow value, Marshall Quotient, Air voids (Vv), Voids in Mineral Aggregates (VMA), Voids Filled with Bitumen (VFB), Retained Stability, were determined by adopting the wet process and compared with neat BC mixes. From the test results, it is clear that the Marshall Test values for modified mixes was much higher as compared to conventional bituminous mixes. Keywords: Bitumen, Aggregate, P.E.T (Polyethylene Terephthalate), Steel slag