The social and economic activity in the 2nd Region of Chile is copper mining, generating subproducts which are eliminated in the environment. It has been reported that in industrialized centers, there is a transference of heavy metals from the mother to the fetus by placental transfer. It's proposed to know the bioaccumulation of copper in organs and fluids of pregnant rats and its effects on the primary ossification centers (POC). Three month female albine rats (Sprague Dowley), are cycled and mated in estrous. On the 8th gestation day, they are injected intraperitoneally with 1 ml of CuSO4 in concentrations 1024, 512, 256, 128, 64 ppm and physiological serum. After 18 days, the female are sacrificed and the fetus evaluated and processing with alizarin red stainig skeleton and histologic technique, 5 mm tissue sections are stained with alcian blue and/or toluidine blue. Maternal blood is obtained, as well as, fetal liver, and fetus, placenta, amniochorion membrane, and amniotic fluid for determining copper levels by means spectrophotometry of atomic absorption. In addition, fetus are checked for external visible malformation. The statistical study was carried out through variance analysis ANOVA, multiple comparison test (LSD), bilateral Fisher test, Kruskal Wallis test. The results show a high and statistically significant levels of copper in fetal liver of the intoxicated groups and control (p<0.01). There are no differences of the chemical in maternal blood, amniotic fluid, amniochorion membrane and placenta between intoxicated and control groups. A significant difference in POC formation in cervical and dorsal vertebras was found with the treatment of 256 ppm compared to the control group (p<0.05). It wasn't observed external abnormalities. It is inferred that copper ion is it's placental transferred to the fetus via placenta bioaccumulating in the liver inducing alterations in the POC formation , specially in cervical and dorsal vertebra level, which microscopically shows absence of characteristic hyaline cartilage tissue