ABSTRACT:The objective of the study was to investigate the effects of supplementing different plant oils to the basal diet on milk yield and milk composition in mid-lactating dairy cows. Forty Chinese Holstein dairy cows averaging 120 days in milk (DIM) at the start of the experiment (body weight = 580 ± 18.2 kg; milk yield = 33.0 ± 2.00 kg/day) were used in a completely randomized block design. The animals were assigned to four dietary treatments according to DIM and milk yield, and supplemented with no oil (control), 2% rapeseed oil (RSO), 2% peanut oil (PNO) and 2% sunflower seed oil (SFO). Milk yield and milk composition (fat, protein, and lactose) were measured. Dry matter intake was similar in all treatments. The supplementation of plant oil increased milk yield, with the highest milk yield in RSO group. Percentages of milk fat, lactose, solids-not-fat and SCC were not affected by treatments except for an increase in milk protein content in oil supplemented groups. The fatty acid (FA) profile of milk was altered by fat supplementation. Feeding plant oils reduced the proportion of both short-chain (C4:0 to C12:0) and medium-chain (C14:0 to C16:1) fatty acids, and increased the proportion of long-chain (≥ C18:0) fatty acids in milk fat. The inclusion of vegetable oils increased the concentration of cis-9, trans-11 CLA. The cis-9, trans-11 CLA content in milk fat was higher from RSO to PNO and SFO was higher than the control. The TVA concentration was higher in the SFO diet, followed by PNO, RSO, and control diets. The results of this study indicated that linoleic acid was more effective in enhancing contents of TVA and CLA in milk fat than oleic acid. No significant effects of week and treatment by week interaction were found out in this study. Overall, feeding plant oils increased monounsaturated and polyunsaturated fatty acids and decreased saturated fatty acids in milk fat. In conclusion, dietary supplementation of RSO increases milk yield the most, while SFO enhances the cis-9, trans-11 CLA content in milk fat more effectively.