Abstract:This study aimed to evaluate the effect of feeding on virgin olive oil (VOO) and extra virgin olive oil (EVOO) at 50% and 100% with or without thyme leaves at 1% and 2.5% on pregnancy and lactation periods. Methods: One hundred and twenty adult female rats (120 ±5g) were randomly divided into 15 groups (n=8) for month before mating. On 19 th day of pregnancy, half of pregnant rats were weighted, killed and their fetuses take off with uterus. Another half of pregnant rats were left to evaluate the lactation period. Biochemical assays, bone measurements and fertility hormones were evaluated. Results: Generally, the VOO groups were improved the health status of pregnant and lactating rats more than EVOO groups. The pregnant rats in VOO and thyme leaves powder groups were lower of body weight gain (BWG) without their fetuses than EVOO and thyme leaves powder groups. The mean weight of fetuses in VOO and thyme leaves powder groups were higher than EVOO combined with thyme leaves groups. Also, the feeding on olive oils with thyme leaves had an increase of number of fetuses and bone Ca and P contents. The results showed that, in an increasing of number of fetuses caused decrease in bone mineral density (BMD). Pregnant and lactating rats fed on 100% olive oils had TC, TG, LDL-C, and VLDL-C lower than the rats fed on 50% olive oils. Also, the rats fed on olive oils and thyme leaves powder had increase in both E2 and progesterone levels before mating and at the end of lactation period compared to control group. Meanwhile, the prolactin hormone levels for rats at the end of lactation period were lower than on 19 th day of pregnancy period. Conclusion: Diet which containing with olive oil improved the health status, especially during pregnancy and lactation periods. Consumption of olive oil and olive oil and thyme leaves could be reduce the risk of infertility in females.