Background: Our previous studies revealed Anethum graveolens L. caused some changes in female reproductive system that induced infertility. Therefore, in this study, oocyte changes as one of probable reasons of infertility were investigated. Methods: In this study, 59 adult female rats were divided into 3 groups of control, low dose (0.5 g/kg) and high dose (5 g/kg) of dill seed aqueous extract (LDE and HDE) treated groups that were gavaged with 1 ml of each dose for 10 days (2 estrous cycles). Vaginal smears were prepared daily. Oocytes of superovulated animals were extracted and their morphometrical changes were measured (n=5). Oocyte cell membrane glycoconjugates were stained with UEA, PNA, and DBA-FITC lectins (n=5). Ultrastructural studies of oocytes were performed using TEM (n=5). The number, weight, and crown-rump length of newborns were examined in three groups after mating with untreated males (n=5). Data were analyzed using SPSS software. Results: Results demonstrated that the duration of the estrous cycle, the diestrus phase and progesterone concentration in the experimental groups increased significantly compared to the control group (p<0.05). Granulosa cells of corpus luteum in HDE-treated group were larger and clearer. The intensity reactions of galactose/N-acetylgalactoseamine terminal sugar of oocyte decreased insignificantly in experimental groups compared to the control group p>0.05. Duration of mating to pregnancy increased and the weight and crown-rump length of newborns decreased in experimental groups significantly (p<0.05). Conclusion: Dill seed aqueous extract can induce infertility without any effect on oocyte structure.