Non-catalytic and catalytic degradation of waste plastics (high-density polyethylene (HDPE), low-densitypolyethylene (LDPE), polypropylene (PP) and polystyrene (PS)) using spent fluid catalytic cracking (FCC) catalystinto liquid product were comparatively studied with a stirred semi-batch reactor at 400oC, under nitrogen stream. Liquidproduct characteristics were described by cumulative distribution as a function of lapse time of reaction, paraffin, olefin,naphthene and aromatic (PONA) composition, and also carbon number distribution on plastic type of reactant. Fordegradation of waste PE with relatively high degradation temperature, the effect of adding spent FCC catalyst greatlyappeared on cumulative distribution of liquid product with a reaction lapse time, whereas those for waste PP and PSwith low degradation temperature showed a similar trend in both non-catalytic and catalytic degradation at 400oC. InPONA and carbon number distribution of liquid product, the characteristics of waste PS that was mainly degraded byend chain scission mechanism were not much altered in presence of spent FCC catalyst. However, waste polyolefinicpolymer that was degraded by a random chain scission mechanism significantly differed on PONA and carbon num-ber distribution of liquid product with or without spent FCC catalyst. The addition of spent FCC catalyst in degradationof polyolefinic polymer, which economically has a benefit in utilization of waste catalyst, significantly improved thelight olefin product by its high cracking ability and also the aromatic product by cyclization of olefin as shape selectivityin micropore of catalyst.