Abstract DMSO (dimethyl sulfoxide) has merits of a high boiling point and high solution power to most photo-resistant materials used in semiconductor and LCD (liquid crystal displayers) industries. Wastewaters originated from the industries contain hundreds of grams of DMSO per cubic mater. DMSO is easily decomposed to DMS (dimethyl sulfide) and DMSO2 (dimethyl sulfone) by microorganisms in biological reactors. Malodorous DMS has a relatively low water solubility and can easily emit into the atmosphere thus causes nuisance problems. The fraction of conversion of DMSO to DMS is possibly related to the volumetric DMSO loading (F/V) to an aerobic wastewater treatment pond. This study aimed to investigate the volumetric DMSO loading which minimize the DMS production. Sequencing batch reaction tests indicate that with F/V of less than 0.45 kg DMSO-S/m3.day, there was no DMS detected in the treating mixed liquor and the vented gas from the liquor. It was also observed that with sulfate-S of higher than 0.55 kg/m3 in the mixed liquor which corresponded to F/V of 0.55 kg DMSO-S/m3.day, a high conversion of DMSO to DMS resulted in the system failure.