The effects of supplementing corn oil (CO) alone or combined with palm kernel oil (PKO) to grazing cows on ruminal fermentation, milk production and its fatty acid (FA) profile were studied. Six multiparous Holstein cows (597 ± 11.5 kg BW, 160 ± 29 d in milk) were assigned to a double Latin square design (3 cows × 3 diets × 3 periods × 2 squares). Three diets were evaluated: a control (C) without oil and 2 with oil addition (720 g/cow/day), one with CO, and the other with CO:PKO (75:25; COKP). Each trial period lasted 28 d (21 for adaptation and 7 for sample collection). Cows strip grazed a Pennisetum clandestinum pasture (3 kg DM/100 kg LW/d) and received daily corn silage (0.9 kg DM), concentrate (4.2 kg DM) and chromium oxide (9 g). Rumen fluid was collected on d 28th, milk samples on d 15, 18 and 21 of each period and feces from d 15 to 21. Milk production was recorded daily. Milk FA and ruminal VFA were determined by GC and Cr in feces and concentrate by AA. Methane production was estimated using ruminal VFA concentration. Data were subjected to ANOVA using GLM procedure of SAS and comparisons among means using Tukey’s test. Voluntary intake and digestibility of the diet were similar among treatments as well as the molar proportions of acetate, propionate, and butyrate. Total VFA (m/L) was lower (C = 94.7 vs CO = 72.2 and COKP = 74.0, P < 0.001) for the diets with oils resulting in lower estimated methane production (P < 0.01). Addition of oils increased milk production (l/d) (C = 21.4 vs CO = 23.6 and COKP = 23.9; P < 0.01) and milk fat (%) (C = 3.15 vs CO = 3.40 and COKP = 3.40; P < 0.05). De novo synthesized FA (g/100 g FA) in milk was higher for the control treatment (C = 68.5 vs. CO = 52.2 and COKP = 58.6; P < 0.01). Conjugated linoleic acid (CLA) (g/100g FA) in milk was higher for the oil diets but decreased by addition of CPK (C = 0.68 vs CO = 1.56, and COKP = 1.01; P < 0.01). Supplementation with CO or COKP in diets of grazing dairy cows increased milk production without affecting voluntary intake or the digestibility of the diet but CO addition resulted in higher milk CLA.