This study investigated changes in Ca balance and BMD during pregnancy in female rats. During pregnancy, the intestinal Ca absorption increased significantly, and Ca accumulation was also markedly elevated. However, BMD values for the lumbar spine decreased significantly during pregnancy. Twenty female SD rats, 10 weeks of age (Japan SLC Co., Shizuoka, Japan) were acclimated for 2 weeks. Then, the rats were divided into two groups; the control (no pregnancy) group (n=10) and the pregnant group (n=10). The rats in the pregnant group were kept in a cage with a male rat for 5 days at 12 weeks of age, and all 10 were successfully impregnated. During the pregnancy period, the values for intestinal Ca absorption and the rate of the intestinal Ca absorption in the pregnant group were significantly greater than those of the control group. In addition, in spite of the significant increase in urinary Ca excretion in the pregnant group, the Ca accumulation was markedly elevated during the latter half of pregnancy. On the other hand, the BMD value in the lumbar spine for the pregnant group significantly decreased during pregnancy. These findings suggest that pregnancy accelerated intestinal Ca absorption and Ca accumulation in female rats, while the lumbar spine BMD decreased during pregnancy.