The present study deals with histological changes of the canine decidual reactions of the endometrium stimulated by intraluminal injection of olive oil with or without scratching injury using a wire. Olive oil caused conspicuous proliferation of the superficial endometrial glands. When olive oil injection was carried out after the scratching, cystic hyperplasia of basal glands as well as proliferation of superficial glands occurred. The results suggest that olive oil stimulates only proliferation of the superficial endometrial glands and the occlusion of the glandular orifices by some stimuli such as the traumatical injury would be needed to induce cystic hyperplasia of the basal glands.