The current knowledge concerning effects of polybrominated diphenyl ether (PBDEs) on benthic aquatic organisms is still very limited although they have been widely used as fire retardant additives for 3 decades. This study was conducted to evaluate the toxic effects of BDE-47 and BDE-183, the two common congeners of PBDEs in river sediments, on a benthic oligochaete worms, Monopylephorus limosus. The worms were exposed to BDE-47 or to BDE-183 for two or eight weeks. The survival rates of M. limosus decreased significantly when exposed to 700 ng/g dry soil of BDE-47 or BDE-183 for 8 weeks, but not in groups of 1-1000 ng/g BDE-47 for 2 weeks. A total of forty proteins of M. limosus has been expressed and determined by the two-dimensional gel electrophoresis (2-DE). Through the cluster analysis, it was found that the protein expression in the group of 100 ng/g BDE-47 was similar to 10 ng/g BDE-183. The results indicate that the toxicity of BDE-183 was greater than BDE-47 to M.limosus. Although the survival rate of M. limosus was not significantly affected when exposed to BDE-47 or BDE-183 at concentrations of 1 to 100 ng/g, significant differences in protein expression were found. Thus, the analysis of protein expression is more sensitive to detect the toxicological change in M. limosus than the survival test.