The purpose of this study was to determine the mercury accumulated at maternal and fetal organs, and compare its levels between maternal and fetal organs on day 20 of gestation, in pregnant Fisher-344 rats which given orally methylmercuric chloride on day 7 of gestation. Pregnant rats were divided four groups by dose: control group, and methylmercuric chloride treatment groups of 10, 20 and 30 mg/kg, respectively. The results obtained are as follows: I The mercury concentrations in maternal organs were the highest in kidney, and followed by blood, spleen, liver and brain. 2. The slopes of regression equation among mercury dose levels in maternal organs were as follows: Kidney 3.62 (r$^2$=0.943), Blood 2.75 (r$^2$=0.941), Spleen 2.49 (r$^2$=0.990), Liver 1.13 (r$^2$= 0.949), Brain 0.33 (r$^2$=0.984). 3. The mercury concentrations in fetal organs and placenta were the highest in liver, and followed by kidney, placenta and brain. 4. The slopes of regression equation among mercury dose levels in fetal organs and placenta were as follows: Liver 1.79 (r$^2$= 0.968), Kidney 0.79 (r$^2$= 0.976), Placenta 0.68 (r$^2$= 0.920), Brain 0.52 (r$^2$= 0.978), All Body 0.58 (r$^2$= 0.941). 5. As to the mercury levels in kidney, dams were 4.8~14.9 times higher than fetus. But as to the mercury levels in liver and brain, fetus were 1.6~2.5 and 1.5~1.9 times higher than dams. In conclusion, the mercury which exposured to pregnant rats can easily pass through the placenta and accumulated in fetus, especially higher in fetal liver and brain.