Abstract: A batch anaerobic test was conducted to examine the biodegradation of decabromodiphenyl ether (BDE209) and 4,4’dibromodiphenyl ether (BDE15) by measuring the accumulative production of methane. The relative activity values were used to determine the inhibition level of polybrominated diphenyl ethers on methanogenic bacteria. The test conditions were that glucose was used as cosubstrate, temperature 35 ℃, COD 10 000—11 000 mg/L and pH 7.0—7.5. The experimental results indicated that there was slight inhibition when concentrations of BDE209 were 0.5, 5, 15, 25, 50 mg/L, respectively. Middle inhibition was observed when concentration of BDE15 was 5 mg/L, but slight inhibition was seen at the rest concentrations.