In order to examine the mutagenicity of cadmium dichloride the author studied the induction of sister chromatid exchanges in chinese hamster ovary $K_1$ cells which treated with cadmium dichloride at various concentrations. The results obtained were as follows : 1. In cells treated with $10^{-4}M$ cadmium dichloride, a small number of cells were viable but no mitosis was bound. 2. The frequencies of sister chromatid exchanges in cells treated with $10^{-5}M;and;10^{-6}M$ cadmium dichloride as $10.7{pm}1.9;and;8.3{pm}2.1$, respectively, were significantly increased for control ($6.0{pm}2.3$). (P<0.05). 3. There were dose-dependent relationship between the concentration of cadmium dichloride and frequency of sister chromatid exchanges in cells treated with cadmium dichloride at concentration ranging from $10^{-5};to;10^{-7}M$.