A study has been carried out on the effect of catalyst acidity and composition (mixtures of base catalyst and catalysts provided with HZSM-5 zeolite of different acidity) on the catalytic cracking of polyolefin pyrolysis waxes carried out under standard conditions in a refinery FCC. The experiments have been carried out in a riser simulator, in the 500-550 °C range. The results show that the yields and composition of product stream are acceptable and controlable by refineries without any special adaptation of process conditions. The acidity of the catalysts has a relevant effect on hydrogen transfer capacity, which contributes to decreasing the concentration of olefins in the gases and in the gasoline. The incorporation of HZSM-5 zeolite is very efficient for increasing the yield of gasoline. This gasoline and LPG are more olefinic than those obtained with the base catalyst, given that hydrogen transfer capacity of the catalyst is inhibited. © 2007 Elsevier B.V. All rights reserved.