Four laboratory-scale anaerobic sequencing batch reactors (ASBRs) were used to treat synthetic wastewaters at COD concentrations of 1000, 800, 600 and 400 mg/liter (BOD5 of 490, 392, 294 and 196 mg/liter respectively). The ASBRs were operated at temperatures of 35, 25, 20 and 15°C. Reactor 1 was operated at a 48-h HRT, reactor 2 at 24-h HRT, reactor 3 at 16-h HRT and reactor 4 at a 12-h HRT. The four substrate concentrations were treated in each reactor and each temperature. Results of the study show 80–90% soluble COD removal efficiency at the various substrate concentrations, temperatures and HRTs, except during 15°C treatment of the more concentrated wastewater at the shorter HRTs. These findings show that the ASBR process could be used for the treatment of low-strength wastewaters at low temperatures, usually treated aerobically with high energy expenditures and large amounts of sludge production.