The secondary cracking performance of gasoline and diesel fractions from the catalytic pyrolysis of heavy gas oil derived from Canadian synthetic crude oil was investigated. Both diesel and gasoline fractions showed poor cracking performance. The feed conversion of the diesel fraction was below 51 wt %, and the yield of total light olefins was below 11 wt %. Meanwhile, the feed conversion of the gasoline fraction was below 30 wt % and the yield of total light olefins was below 7 wt 96. The selectivity of total light olefins at 660 degrees C was only 22% for both fractions, and the selectivity of dry gas at 660 degrees C reached 25% for the diesel fraction and 34% for the gasoline fraction. The selectivity of coke at 660 degrees C reached 26% for the diesel fraction and 16% for the gasoline fraction. The diesel and gasoline fractions could partly crack to lighter components and could partly condense to heavier components. The condensation reaction played an important role in catalytic pyrolysis, and the selectivity of condensation products at 660 degrees C reached 42% for the cracking of the diesel fraction and 55% for the cracking of the gasoline fraction. The monomolecular cracking is the predominant cracking type, and both the free radical and the carbonium ion mechanisms play an important role under the experimental conditions.