The influence of a single dose of different plant oils on the rat estrous cycle and fertility was studied. The ovary function activity was ascertained to be inhibited by soybean, peachy or buckthorn oil injection which resulted in the prolongation of the estrous cycle and its phase destruction. The administration of oil provoked temporal fecundation retain (corn, soybean, sunflower-seed or peachy oils) and decreased the number of pregnant animals (peachy, olive or sunflower-seed oils). The number of the ovary corpus luteum, placentas and living fetus in the uterus were declined, and embryonic death was increased in females after peachy, corn, sunflower-seed, soybean, castor or buckthorn oil feeding. It is concluded that vegetable oils depress ovarian folliculogenesis and have not only anti-implantative, but abortive effects to a greater or lesser extent.