Abstract: To explore the effect of arsenic to immunefunction by measuring anticomplementary competence (ACC) in sera of rats.The ACC of rats arsenic poisoning was significantly lower than that of the control rats(P<0.05).The ACC of arsenic+selenium group were significantly higher than that of arsenic group(P<0.05), and had no significant difference with control group(p>0.05). There was no significant difference in sera ACC between the two arsenic+selenium group(p>0.05).These results suggested that the lower ACC might be one of the mechanism responsible for the disorder of immune adjustment induced by the arsenic poisning,and the selenium could have a toxicopexis effect.