-The effect of supplementation with corn oil (CO) and its mixture with palm kernel oil (CO:PKO 75:25) to grazing cows on ruminal fermentation, milk yield, and its fatty acid (FA) profile was evaluated. The treatments were: one control treatment (C) without oil and two treatments with 720 g d −1 /cow of CO or CO:PKO (ether extract: 22.7 g kg −1 for control treatment, 66 g kg −1 for CO, and 65 g kg −1 for CO:PKO). Six multiparous Holstein cows (6.3±1.8 yr, 597±11.5 kg body weight (BW), 160±29 d in milk; mean ± standard deviation) were assigned to a double 3 × 3 × 3 Latin square design. Cows grazed (3 kg DM/100 kg BW) a Cenchrus clandestinus (previously Pennisetum clandestinum) pasture and were supplemented with 0.9 kg d −1 DM corn silage, 4.2 kg d −1 DM concentrate, and 9 g Cr 2 O 3 . The mixture of concentrate and oils was offered twice a day. The addition of oils increased milk yield (kg d −1 ) (C: 21.4, CO: 23.6, CO:PKO: 23.9) and milk fat concentration (g kg milk −1 ) (C: 31.5, CO: 34.0, CO:PKO: 34.0). Compared with control, conjugated linoleic acid (18:2 c9 t11 CLA) proportion (g 100 g −1 FA) in milk fat was higher for oil treatments (C: 0.68, CO: 1.56, CO:PKO: 1.01). Voluntary intake and digestibility were not different among treatments. The molar ratio of acetate, propionate, and butyrate was not different among treatments, but the molar concentration of volatile fatty acids (VFA) was lower for CO and CO:PKO, resulting in a lower estimated methane (CH 4 ) production (mL/100 mol VFA) for CO and CO:PKO treatments. Supplementing CO and CO:PKO to grazing dairy cows increases milk yield without affecting voluntary intake or diet digestibility. The proportion of conjugated linoleic acid increases more for CO than for CO:PKO.