Pregnancy anemia and pregnancy-induced hypertension (PIH) are common and potentially dangerous disorder in human pregnancy, and nutritional status of pregnant women is one of the leading causes. Chlorella contains large quantities of folate, vitamin B-12 and iron, and can help improve anemia and hypertensive disorder. Our objective was to investigate the preventive effects of Chlorella supplement on pregnancy anemia and PIH in Japanese pregnant women. A total of 70 pregnant women were placed into the control group (n = 38) or the Chlorella group (n = 32). The subjects in the Chlorella group were supplemented daily from 12th–18th wk of gestation until delivery with 6 g of Chlorella supplement. The proportion of anemic (hemoglobin level < 11 g/dL) subjects in the Chlorella group were significantly lower compared with the control group at the second and third trimesters. Additionally, in the Chlorella group, the incidences of proteinuria and edema, signs of PIH, were significantly lower during the third trimester. These results suggest that Chlorella supplementation significantly reduces the risk of pregnancy associated anemia, proteinuria and edema. Chlorella supplement may be useful as a resource of natural folate, vitamin B-12 and iron for pregnant women.