The effects of sulfide, sulfite and sulfate on degradation of volatile fatty acid (VFA) in UASB process have been studied by using serum bottle assay and septage-leachate acclimated biogranules. The relative toxicity of the compounds towards methane production and degradation of total VFA varied as SO42--S > S2- > SO32--S and SO42--S > SO32--S > S2-, respectively. The difference of this order shows the importance of choosing monitoring factor in evaluating the effect of sulfur compounds on a UASB system. For the individual VFA the effects of sulfur compounds depended on the types of VFA. The VFA-degrading activity of anaerobic biogranules was decreased by 50% when 34,26 and 20 Mg of S2-, SO32--S and SO42--S were added to each gram of biomass, respectively. A comparison of the toxicity-resistance between two different anaerobic biogranules that acclimatized with septage-leachate mixture and septage was also made. In the presence of the leachate, the toxicity-resistance of biogranules was not weakened to sulfide and sulfate but was enhanced to sulfite.