This study is the first attempt to investigate heavy metal concentrations in the soldier crab with a view to it being a potential candidate for the monitoring of copper(Cu), zinc(Zn), nickel(Ni), lead(Pb) and cadmium(Cd) levels on the western coast of Taiwan. The objectives of this investigation included the following: (1) to assess the pollution status at different sites by determining the metal concentrations of ambient water and Pacific oysters; (2) to monitor the concentrations of heavy metals, including Cu, Zn, Ni, Pb and Cd, in the soldier crab; (3) to assess the effect of sex, wet weight and reproductive season at different sites¡F(4) to investigate the distribution of metal concentration among carapace, gonads, midgut gland, muscle; and (5). to assess the pollution status at different sites and years by monitoring the concentration of heavy metals, including Cu, Zn, Pb and Cd in male soldier crabs The Pacific oyster and stream results proved that site B is contaminated by Cu, Zn and Pb from streams B-1 and B-2. The highest Cu, Zn, Ni and Pb concentrations in soldier crabs appeared at site B, and significant differences in the accumulated concentrations of Cu, Pb, Zn and Ni in soldier crabs were found between the sites tested. The highest bioconcentration factors of Cu, Zn, Ni and Pb in soldier crabs appeared at site B, indicating that the soldier crab can accumulate Cu, Zn and Pb to the same degree as the Pacific oyster. In fact, soldier crabs can accumulate more Ni than Pacific oysters, better reflecting the conditions of the ambient environment. These phenomena, as well as the fact that the soldier crab is able to accumulate relatively high levels of Cu, Zn, Pb and Ni, suggest that this crab is a potential biomonitor of Pb and Ni pollution in aquatic ecosystems. Only in the case at site A of Pb sex related difference could be detected. In general mean Pb level in male soldier crabs were higher than in female. There are no significant sex related differences of Cu, Zn, Cd and Ni in soldier crab among three sites. The lead mean concentration in reproduction season and pre- reproduction season were higher than non-reproduction seasons. The highest concentrations of lead were found in carapace and the gonad in reproduction season. The results presented that the metal concentration in soldier crabs vary significantly not only because of season change in polluted sites, but also it may be influenced by the sex-related and size-related difference of organisms. After eliminating size effect, sex effect by analyzing 0.7 g~ 1.0 g and male soldier crabs to monitor the pollution status, the Cu and Zn concentrations in soldier crabs along the Changhua coastline(site A and site B) is stable¡F The higher concentrations of Pb and Cd in soldier crabs existed in 2002 and 2003. We suggested that the polluted sources of Pb and Cd along the Changhua coastline in 2002 is abundant, and of Pb contents from 2003 to 2006 and Cd content from 2003 to 2007 are decreasing. Therefore, it is essential to take size effect, sex, season, and polluted status into account in comparative biomonitoring studies using soldier crabs as metals biomonitor. The baseline concentration of soldier crabs were 21.4 £gg g-1 wet wt. Cu, 20.1 £gg g-1 wet wt. Zn, 0.13 £gg g-1 wet wt. Pb, 0.12 £gg g-1 wet wt. and 0.91 £gg g-1 wet wt..