This study investigates the generation and fate of volatile organic sulfur compounds (VOSCs) during biodegradation of waste activated sludge under anaerobic conditions. Experiments involved the operation of laboratory-scale anaerobic digesters at a solid retention time of 20 d. Concentration profiles of methanethiol, dimethyl sulfide (DMS), dimethyl disulfide, and hydrogen sulfide were monitored. Methanethiol (MT) and DMS are the main organic sulfur compounds exhibiting consecutive increase/decline phases. In the second step, aliquots taken from bioreactors were supplemented with two sulfur-containing amino acids, cysteine, and methionine. The results suggest that the biodegradation of the two sulfur-containing proteins are the primary source of hydrogen sulfide, methanethiol, and DMS generation. Finally, ethyl-2-butynote was added to aliquots taken from the bioreactors to explore the role of methanogenic activity. Methane production is stopped, and resulting MT and DMS profiles are no longer included as a declining phase. The results suggest that sulfur amino acids are a potential primary source for the formation of MT and DMS that were subsequently degraded by methanogens. Therefore, reducing proteins containing sulfur amino acids along with increasing methanogenic activity appears to be an effective strategy to control VOSCs and the associated odor problem.