The purpose of this study is to observe the optimium effects of cadmium chloride on the rat fetus. Cadmium chloride 5 mg/kg was administered intraperitoneally once to the pregnant rats on GD10.5, and the rats were sacrificed on GD 17.5 followed by formalin fixation for bone-cartilage counterstaining, Bowin fixation for palate observation and fixation with 5% glutaraldehyde solution for SEM. The results were as follows; 1. In the cadmium chloride treated group, the survival rate of rat embryos was 65.7% and the average body weight was 589+/-77.5 mg. Both were significantly lower statistically than those of the control group. 2. In the cadmium chloride treated group, craniofacial anomalies such as hydrocephalus, hemorrhagic bullae and cleft palates, and anomalies of the limbs such as polydactyly and oligodactyly were observed. 3. In the cadmium chloride treated group, no primary ossification centers were found in all fetuses. In the vertebral column and the ribs, congenital anomalies such as fusion of vertebral laminae, short tail, fused ribs, division of ribs, accessary rib and loss of rib were observed. 4. In the cadmium chloride treated group, congenital anormalies of the ribs were predominently on the right side and that of the feet were predominently on the left side. 5. In the cadmium chloride treated group, a protein with molecular weight of 14.1 kDa was disappeared in the forelimbs and hindlimbs of GD12.5, and proteins with molecular weight of 14.1 kDa and 30.2 kDa were decreased in the forelimbs of GD13.5, and a protein with molecular weight of 14.1 kDa was disappeared in the hindlimbs of GD13.5, and a protein with molecular weight of 14.1 kDa was decreased in the hindlimbs of GD13.5. With the above results, it is considered that cadmium chloride causes death in utero due to direct acute poisoning of the rat fetuses, inhibits development of skeletal system, and induces various congenital anomalies. And the action mechanisms of cadmium chloride may be the cause of the destruction of capillaries in CNS as well as the inhibition of carbonic anhydrase. But this is still not confirmed.