The objective of this study was to determine the effects of Savlon, Gluataraldehyde and Sodium Hypochlorite on Performance of Sequencing Batch Reactor. Three lab scale reactors of 12 litres in volume were used to treat synthetic wastewater contained different disinfectants. Reactor No. 1 was fed with synthetic wastewater and Savlon . Reactor No. 2 and No. 3 were fed synthetic wastewater mixed with Glutaraldehyde and Sodium Hypochlorite respectively. The sludge retention time ( SRT ) was controlled at 3, 5, 10 and 15 days. The concentration of disinfectants were increased gradually from 20 ppm. to 40, 80, 160, 320 and 640 ppm. every 10 days or until the system failed to operate. The results indicated that after adding disinfectants into the system, the removal efficiency of COD and nitrogen were decreased when the disinfectant concentrations were increased. At concentration level of 80 ppm, the system started to failed. Moreover the effect of disinfectants concentration on settling characteristics of sludge was observed. Pin floc in the effluent was appeared at the high concentration level. At SRT of 15 days, the highest removal efficiency of COD and nitrogen were obtained and the system could tolerated to the highest concentration of 640 ppm. The disinfectants were not affected significantly for the removal efficiency of phosphorus. However at the short SRT, the highest removal efficiency of phosphorus was observed. The study of the effect of 3 disinfectants on kinetic constant in batch system found that the values of Y, k and mm were decreased with the concentration level increased. The values of kd and KS were increased when concentration increased.