Abstract: Objective To investigate the effects of metal exposure on defecation behavior in nematode Caenorhabditis elegans. Method The concentrations of CdCl2, CrCl2, HgCl2, and Pb(NO3)2 metal solutions used were 50 µmol•L-1, 100 µmol•L-1, 150 µmol•L-1, and 200 µmol•L-1, respectively. The endpoint of mean defecation cycle length was used to evaluate the metabolism state in metal exposed nematodes. The linear regression analysis was performed to investigate the possible associations for the concentration of exposed metals with mean defecation cycle length, and between pumping rate and mean defecation cycle length. Results Exposure to Hg and Pb at all concentrations and exposure to Cr and Cd at concentrations from 100μmol•L-1 to 200 μmol•L-1 induced a significant increase of mean defecation cycle length. Alterations of mean defecation cycle length in metal exposed nematodes exhibited a concentration-dependent manner. In addition, mean defecation cycle length was significantly correlated with the concentrations of exposed metals tested. Moreover, the close association between pumping rate and mean defecation cycle length could be formed in metal exposed nematodes. Furthermore, the toxicity on defecation behavior from exposure to Hg and Pb was more severe than that from exposure to Cr and Cd in nematodes. Conclusion The endpoint of mean defecation cycle length can be used to effectively evaluate the toxicity on metabolism state from metal exposure, and the close association of mean defecation cycle length with pumping rate can be observed in metal exposed nematodes.