Wastewater from a slaughtering house was treated by an anaerobic baffle reactor (ABR). The effects of variable loads on the operating performance of the ABR were studied. The results show that the ABR was very stable with respect to shock loading due to its special structure. The change in COD removal efficiency was less than 5% when the influent COD concentration was kept between 2 500~3 000 mg/L and the HRT decreased from 27.5h to15h. When HRT was kept for 20h and the influent COD concentration increased from 2 500 mg/L to 4 800 mg/L, COD removal efficiency only decreased by 69% the second day after the load change.