Abstract: The organic matter associated with Fankou Pb-Zn deposit(Northern Guangdong province, southeastern China) has been studied by petrographic，organic petrology，elements analysis and gas chromatographic methods, The host rocks of the deposit are abundant in organic carbon ranging from 0.03％ to 0.4％ ．The vitrinite reflectances (R0) are determined as 1.92％-3.55％ ，mostly above 3.0％ ．It is suggested that the maturity of the organic matter is high and most of the organic matter has become bitumen．The character of saturated hydrocarbons，extracted from host rocks and ores (Pr and Ph)shows a marine-facies reduction condition．Gas chromatographic analytical results show that the 0rganic matter in orebody experienced thermolysis and thermal metamorphism，and thus the formed CH4 and kerogen acted as reducing agents to reduce sulfate to sulfide hydrogen，which was favorable for precipitation of metal sulfides． In addition，the occurrence of pyrite in granular and “strawberry" form indicates the effect of bacteria and micro-algae during early sedimentation．