The objective of this study was to investigate the effect of dietary supplementation of Zn-L-selenomethionine (Zn-L-SeMet) on lactation performance and metabolic status of dairy cows at peak lactation period. Sixty multiparous Chinese Holstein dairy cows at peak lactation were selected. The cows were divided into 15 blocks with four cows in each block based on the similarity principles of the lactation time, body mass, parity and milk yield. The four cows in the same block were randomly assigned to four treatments: the control group (fed with basal diet, without supplementing Zn-L-SeMet), and Zn-L-SeMet supplementation groups (supplementing Zn-L-SeMet with 0.1, 0.2, 0.3 mg/kg Se, respectively, which was calculated in dry matter mass). The prefeeding period was two weeks, and the experiment lasted for 12 weeks. The results showed that: 1) the energy corrected milk, milk, milk fat, milk protein, milk lactose yields and feed efficiency of dairy cows increased linearly (P0.01) as the supplementation of Zn-L-SeMet increased; 2) the milk fat and lactose contents, and Se concentration in milk were improved linearly or quadratically, and the milk protein content was decreased linearly (P0.05) by administrating increasing amount of Zn-L-SeMet; 3) the activities of glutathione peroxidase and catalase in plasma were improved linearly or quadratically (P0.05) and malondialdehyde content in plasma was decreased linearly or quadratically (P0.01) with the increase of Zn-L-SeMet supplementation. The above results demonstrate that dietary supplementation of Zn-L-SeMet can effectively improve the performance and antioxidant capacity of dairy cows during the peak lactation. It is suggested that Se from Zn-L-SeMet can be effectively used by lactating cows, and Zn-L-SeMet is an effective dietary Se source.