A blend containing 20 wt.% low density polyethylene (PE) and 5 wt.% polyvinylchloride (PVC) in heavy vacuum gas oil was pyrolyzed at 623 K (dechlorination step). This mixture was then thermally and catalytically cracked in the presence of hydrogen at 673-723 K in a batch reactor (hydrocracking step). The liquid products from hydrocracking contained no chlorine compounds although the chlorine amount in the dechlorinated mixture was 700 ppm. Experiments have shown that the dechlorination step and the temperature had great effect on the product distribution from the hydrocracking step. It was observed that the dechlorination step led to both degradation of PE and dechlorination of PVC and that PE could be completely cracked with/without a catalyst by hydrocracking even though at 673 K. The use of a catalyst decreased the gas yield and led to an increase in coke yield at 723 K. The effect of the catalyst on the boiling point range of liquid product obtained from hydrocracking depended on the reaction temperature. The chlorine compounds in dechlorinated mixture affected the catalytic activity of the catalyst especially at 723 K. 75% and 55% of the liquid products obtained at 723 K with and without a catalyst, respectively, were hydrocarbons having boiling points ranging from 323 to 473 K.