The aim of the present study was to evaluate the developmental toxicity of silicon dioxide nanoparticles (SiO₂NPs) using high doses to maximize the possibility of detecting any potential risk on fetuses. Treatment with SiO₂NPs subcutaneously from gestational day 7 to day 20 at the doses 50, 125 or 250 mg/kg body weight/day did not alter the numbers of implantation sites or live fetuses. No teratogenicity or embryolethality has been observed at any dose level, although deficits in fetal body weight and in skeletal development were noted in the rat treated with the doses 125 and 250 mg/kg body weight. Therefore, SiO₂NPs-induced maternal toxicity. The maternal toxicity was consisted of significant reduction in maternal body weight gain, anemia with elevation in platelet numbers, leukocytosis (increased neutrophils and lymphocytes), splenomegaly and an increase in the relative placental weight with varying degrees of inflammation in the basal and labyrinth zones. These results indicate that SiO₂NPs are minimally-embryotoxic at maternally-toxic doses.