The nulliparous female (12 weeks old, ddN strain) were used. The mice were intra-peritoneally administered with single injection of NiCl2 solution on the day 7, 8 and 9 of gestation. Four different levels of dosis were injected as follows : namely 2.2, 3.3, 4.5, and 5.6mg/kg (as Ni) which correspond to 1/10, 1.5/10, 2.0/10 and 2.5/10 of LD50 of adult mice respectively. The mothers were killed on the day 18 of gestation and their uteri were examined for implantation and resorption sites. Each fetus was weighed and examined for external anomalies. Skeletal preparations staind with Alizarin Red were also examined. The higher the dose increased, the more the resorptions and fetal deaths occurr ed among groups injected with NiCl2. Fused ribs and/with fused vertebral relationships archs were observed among groups injected with NiCl2 according to positive dose-response and those occupied 79 % out of malf ormatons as a whole. The highest rates of skeletal anomalies were observed in the case of groups injected on the day 9 of gestation compared with the groups injected on the day 7 or 8 of gestation at any level of dosis. Retardation of process in ossification was observed among fingers, toes, taluses and calcaneuses. Though the number of mother mouse is not sufficient, the incident rate of anomalies of fetal mice was so remarkable that the existence of teratogenic action of Ni can be proved. And through the experiment, it can be said that there exist developmental stage specificity to the action of Ni and agent specificity for the adverse influence to the fetal mice. There must be performed further detailed observation to make more statement on this theme.