In the present study, we examined the relationship between average fish consumption, as well as the type of fish consumed and levels of mercury in the blood of pregnant women. We also performed follow-up studies to determine if blood mercury levels were decreased after counseling and prenatal education. To examine these potential relationships, pregnant women were divided into two groups: a study group was educated to restrict fish intake, whereas a control group did not receive any prenatal education regarding fish consumption. We measured blood mercury level and performed follow-up studies during the third trimester to examine any differences between the two groups. Out of the 63 pregnant women who participated in our study, we performed follow- up studies with 19 pregnant women from the study group and 12 pregnant women from control group. The average initial blood mercury level of both groups was 2.94 microg/L, with a range of 0.14 to 10.75 microg/L. Blood mercury level in the group who ate fish more than four times per month was significantly higher than that of the group who did not consume fish (p = 0.02). In follow-up studies, blood mercury levels were decreased in the study group but slightly increased in the control group (p = 0.014). The maternal blood mercury level in late pregnancy was positively correlated with mercury levels of cord blood (r = 0.58, p = 0.047), which was almost twice the level found in maternal blood. Pregnant women who consume a large amount of fish may have high blood mercury levels. Further, cord blood mercury levels were much higher than that of maternal blood. Because the level of fish intake appears to influence blood mercury level, preconceptual education might be necessary in order decrease fish consumption.