Silicon crystal 2-5 nm nanoparticles in the form of 1-5-μ granules in water suspension were injected intraperitoneally in a single dose to male F(1)(CBA×C57Bl/6) mice or to outbred albino rats on days 1, 7, and 14 of gestation. Silicon crystal nanoparticles in doses of 5, 25, and 50 mg/kg exhibited no cytogenetic activity in mouse bone marrow cells after 24-h exposure and in doses of 5 and 25 mg/kg after 7 and 14-day exposure. A 24-h exposure to silicon nanoparticles in a dose of 5 mg/kg significantly increased DNA damage (detected by DNA comet assay) in bone marrow cells. In a dose of 50 mg/kg they considerably increased DNA damage in bone marrow and brain cells after exposure of the same duration. Silicon nanoparticles in doses of 5 and 50 mg/kg caused no genotoxic effects in the same cells after 3-h and in a dose of 5 mg/kg after 7-day exposure. Silicon crystal nanoparticles in a dose of 50 mg/kg caused death of 60-80% mice after exposure <24 h. Injected in a dose of 50 mg/kg on days 1, 7, and 14 of gestation, silicon crystal nanoparticles reduced body weight gain in pregnant rats and newborn rats at different stages of the experiment, but had no effect on other parameters of physical development of rat progeny and caused no teratogenic effects.