The main aim of this study was to investigate the effect of red mud on the decomposition and dechlorination of waste plastics. Thermal and catalytic degradation of a mixture of municipal waste plastics (MWP) and heavy vacuum gas oil (HVGO) into fuel oil was carried out by a onestep and a two-step process. One-step processing was performed at 430 degreesC by stepwise pyrolysis. Red mud (RM) was used as a dechlorination catalyst. In two-step processing, degradation in the presence and absence of solid acid catalyst (silica-alumina, SA1) was carried out at 430 degreesC followed by dechlorination in a flow-type fixed-bed reactor at 350 degreesC over RM. Copyrolysis of MWP with HVGO led to a synergic effect, increasing the liquid yield. TR99300 had a good dechlorination effect in two-step processing, however it was not effective for MWP/HVGO mixture. In both processes, RM was very effective in the sorption of both inorganic and organic chlorine compounds. Hydrogen chloride (HCl) formation from the degradation of poly(vinyl chloride) (PVC) in MWP was depressed by RM. In one-step processing, the yield of liquid products from the degradation of MWP in HVGO was about 70 wt %. The chlorine content of the liquid product was 1127 ppm in the absence of RM, whereas it decreased to the very low level of 90 ppm in the presence of RM. We obtained oil having a negligible amount of chlorine using TR99300 and RM in the two-step process. The carbon number distribution of liquid products was similar in both processes. The liquid hydrocarbons derived from the degradation of MWP/HVGO were distributed in a wide range of carbon number (C-5-C-25) With a big peak at C-9.