The aim of this study was to determine the effects of body weight, organ weight, hematological values and biochemical parameters by estrogen on the ovariectomized (OVX) rats. The animals were divided into 4 groups. Intact group (n=10) received no treatment and operation. Sham group (n=10) received only sham operation and no treatment. OVX group (n=10) received operation and no treatment. OVX+E2 (n=10) received operation and estrogen. The body weight of each group increased, but that of OVX+E2 group decreased. There were very significant differences (P?0.001) of body weights between OVX+E2 group and the other groups. Also, the wight of important organs such as heart, liver, spleen and kidney was measured. The heart weight was significantly lower (P?0.05) in the OVX+E2 group than the Intact group. The liver weight of the OVX+E2 group was significantly different in comparison with those of the other groups. On the other hand, there were no significantly differences in the organ weight of spleen and kidney between the OVX+E2 group and the other remaining groups. The hematological values of WBC, RBC, MCV, MCH and MCHC were not significantly different among the groups. The serum total protein and albumin decreased significantly in the OVX+E2 group as compared to those in the intact group. But, there were no significant differences in Ca, IP and Mg among the groups. We conclude that estrogen was significantly decreased the body weight in the ovariectomized rats. Our findings suggest that estrogen may influence the process of lipid packaging and absorption in the ovariectomized rats.