Abstract: The Russian sour crude Atmospheric Residuum (AR) FCC experiments were performed in fixed fluidized bed reactors in order to investigate its catalytic cracking characteristics and the sulfur distribution in products. The results showed that its catalytic cracking characteristics are similar to the normal AR. Reaction temperature had less effect on light oil productivity, while the light oil productivity decreased with increase of catalyst-to-oil ratio. During catalytic cracking, 40% of sulfur content in Russian sour crude AR became smaller sulfur compounds such as H2S, 25% of that distributed in diesel as thiophene and its derivatives, 10% of that distributed in coke, only 4%～6% of sulfur compounds such as sulfide and thiol distributed in gasoline. Sulfide and thiol are easy to be deprived as conversing into lighter sulfur compounds such as H2S. Hence sulfur content in gasoline decreased with increase of reaction temperature and catalyst to oil ratio, while the sulfur content in diesel showed reverse tendency because thiophene and its derivatives hardly decomposed under the cracking conditions. When the yield of light oil reached to 63.38%, sulfur concentration was 1197.82 mg/kg in gasoline and 18700.79 mg/kg in diesel oil at 520 ℃ and catalyst-to-oil ratio of 6. Therefore, it is difficult to get better desulfurization effect through optimizing the cracking conditions. The catalyst with desulfurization activity should be used to make much more sulfur content converse to smaller sulfur compounds such as H2S, and then the cleaner light oil with less sulfur could be produced.