Objective: So opiate consumption has unfavorable consequences on different organs we decided to evaluate the effects of morphine on the uterus structure. the present study focused on the probable effects of morphine on histological structure of uterus in Balb/c mice. Materials and Methods: Forty Balb/c female mice were provided for this study. Each three females mice were crossed with one male and vaginal plaque was considered as zero day of pregnancy (E0). Nonpregnant mice were displaced by other females with vaginal plaque. The pregnant females were divided into four groups(two experimental and two control groups). Five mg/kgw for experimental group number1 and ten mg/kgw for experimental group number2 morphine were injected intraperitonealy (IP) (every day during 15 days) in each experimental group respectively. The same volume of saline was used for IP injection in the first control group and the other control group did not receive any injection. In the fifteenth day of gestation (E15) the pregnant females were sacarified and their uteri were removed. After tissue processing hematoxylin-eosin staining was done and all of the samples were studied using light microcopies.400sections from 40 mice were provided and microscopically scrutinized for finding the changes such as cell infiltration vascular congestion and necrosis. Data was analyzed based on chi square and fisher tests. Results: In light microscopy our data showed the uteri of control groups were normal but in experimental groups our findings were some picnotic cells inflammatory cells infiltration and congestion of blood vessels. The percentage of inflammatory cells infiltration and picnotic cells were 60% in the first experimental group70% in the second and 0% in both the first and second control groups. The percentage of blood vessels congestion in the experimental groups (1 &2) was 70 % and 0% in the control groups(1&2). according to our findings There was a significant difference between the experimental and control groups (p=0.0001). Conclusion: data indicated the morphine administration caused histologic lesions that may be responsible for abortion or infertility.