Coke removal by oxidative treatment was investigated for a number of HY zeolites with framework Si/Al ratios of 4-100, coked at different levels (from 2 to 20 wt%) during propene transformation at 450-degrees-C. A strong influence of the density of framework aluminium atoms hence of the density of the acid sites was found. On the other hand the content of the zeolite in extraframework aluminium species as well as the composition of coke were of minor importance for coke removal. A mechanism involving radical carbocations as intermediates is proposed.