The experiment was conducted to determine the effects of nicotinamide on the metabolism of carbohydrate, lipid, protein, and the ion chroma in serum of Chinese Holstein cows under the heat stress condition. Twenty healthy early lactation Holstein cows were randomly assigned to the control and nicotinamide supplementation group for a 10-week experimental period. Cows were fed with basic diet or basic diet plus 8 g·d^-1 nicotinamide in the control or nicotinamide group, respectively. The results were as follows. (1) The concentrations of nonestesterified fatty acid, total triglyceride, total cholesterol, and low density lipoprotein cholesterol significantly decreased in the nicotinamide supplementation group (P<0.05) and the level of β-hydroxybutyricacid also showed the decreasing trend (P = 0.1); however, supplemented with nicotinamide had no significant effect on the levels of serum glucose, total protein, albumin, and urea nitrogen; (2) Compared to the control group, the levels of sodion, calcium, and chloridion ion in serum significantly increased by nicotinamide supplementation, but no significant difference in the levels of kalium, magnesium, and phosphonium between the two groups was observed (P<0.05); therefore, nicotinamide supplementation at 8 g·d^-1 showed the best effect on improving the lipid metabolism and