Abstract: Decalin cracking over Y and ZSM-5 zeolites were conducted in a small fixed fluidised bed (FFB) reactor; the effect of temperature and catalyst/oil ratio on the opening of naphthenic ring in decalin cracking over Y zeolite was investigated. The results showed that the products of decalin cracking over zeolite catalysts by naphthenic ring opening involve non-aromatics (propane, propylene, butane, butylenes, methylpenptane, cyclopentane, cyclohexane, etc.) and monocyclic aromatics (benzene, and C_1~4 alkyl benzene); polycyclic aromatics (tetrahydronaphthalene, naphthalene, alkyl naphthalene, phenanthrenes, pyrenes, etc.) and even coke may also be formed through dehydrogenation condensation reactions. The selectivity for naphthenic ring opening over ZSM-5 catalyst is higher than that over Y catalyst, due to difference in the diffusion and adsorption of naphthenic hydrocarbon on two catalysts. The relative ratio of naphthenic ring opening to dehydrogenation condensation reactions (NRO/DHC) is higher over ZSM-5 catalyst than that over Y catalyst. Under the conditions of 450~550 ℃, weight hourly space velocity of 10 h^-1, and catalyst/oil mass ratio of 3~9, with the increase of the reaction temperature or the catalyst/oil ratio, the bimolecular hydrogen transfer and dehydrogenation condensation are enhanced and as a result, the selectivity to the products from naphthenic ring opening is decreased.