Eight Chinese Holstein cows were used in a 4×4 Latin square design to determine the effects of rumen protected methionine (RPMet) and Niacin on milk yield and milk composition of lactating cows with 14 d adaptation and 6-d sampling periods. The cows were fed the control diet or the control diet plus RPMet tion in the diet increased 4% fat corrected milk (FCM) yield (P0.05). Dietary niacin supplementation increased milk yield (P 0.05). RPMet supplementation in the diet of lactating cows significantly decreased serum urea nitrogen (P0.05).