The adverse effects of salt on biological treatment of saline wastewater inoculated by activated sludge culture were investigated. A synthetic wastewater composed of diluted molasses, urea, KH2PO4 and various concentrations of salt (1-5% w/v NaCl) was treated in an aerobic-biological reactor operating in fed-batch mode. An activated sludge culture obtained from a wastewater treatment plant was used as the seed. Variations of chemical oxygen demand (COD) removal rate and efficiency with salt concentration were determined. A rate expression including salt inhibition effect was proposed and kinetic constants were determined by using the experimental data.