The objective was to examine effects of plant oil supplement on uterine health, ovarian function, and oocyte characteristic in heat-stressed dairy cows. Prepartum cows (n = 36) were randomly allocated to one of 3 dietary treatments; control, 4% refined palm oil (PO), and 4% refined sunflower oil (SO). ANOVA using the general linear model procedure was performed to determine treatments effect. All variables were analyzed with a nested ANOVA with treatment, animal (treatment), and time included in the model. Differences between specific means were evaluated by least significance difference. Placental expulsion and uterine involution in cows fed oil supplements occurred earlier than control cows (3.4 h and 33.2 d for cows fed SO, 4.9 h and 42.0 d for cows fed PO, and 21.0 h and 50.4 d for control cows; P < 0.05). Numbers of class 1 (2–5 mm) and class 3 (≥10 mm) follicles of cows fed oil supplements were greater than those of control cows (P < 0.05). In the second experiment, lactating cows (n = 42) were hormonally synchronized and were randomly offered diets supplemented either with 4% PO or 4% SO for 42 d. Follicle and oocyte numbers and corpus luteum (CL) volume were determined on d 5, 9, and 13 of the estrous cycle and morphologic quality assessed. Neither follicle nor oocyte characteristics were affected by the dietary treatment, however volume of CL and progesterone concentrations on d 13 in cows fed SO were greater (P < 0.05) than those fed PO diet (8,290 vs. 7,875 mm³ and 5.0 vs. 3.9 ng/mL). The data support the beneficial effects of SO supplement in diet on reproductive function in dairy cows