Biological treatment is a very promising method used in treating organic-containing wastewaters because of its low treatment cost without environment impact. In this study, aerobic sequencing batch reactors (SBR) were used to study the biodegradation of the dilute biodiesel wastewater stream of the biodiesel production unit which spent vegetable oils were reacted with ethanol using NaOH as the catalyst. The sludge taken from the activated sludge plant treating biodiesel wastewater was used as the seed sludge to start the studied SBR units. The SBR units, having an effective volume of 1.5 L, were operated on a fill-and-draw basis with four cycles per day at different chemical oxygen demand (COD) loading rates (0.05–0.60 kg/m³d)under room temperature (25–27°C). Since the studied wastewater was lacking nitrogen and phosphate, ammonium hydrogen carbonate (NH₄HCO₃)and di-potassium hydrogen orthophosphate (K₂HPO₄)were added as supplement for the enhancement of biodiesel wastewater biodegradation. The results showed that when the COD loading rate increased, the removal efficiency decreased. Under the studied conditions, a maximum COD removal of 91.4% and total organic carbons (TOC) removal of 35.7% were achieved at the lowest COD loading rate of 0.05 kg/m³d. Moreover, the minimum food/microorganism (F/M) ratio and the highest mixed liquor suspended solids (MLSS) were found to correspond to the lowest COD loading rate of 0.05 kg/m³d.