Objective To explore effects of zinc on the contents of cycl in D2, cycl in-dependent kinase 4 (CDK4), and their DNA and total cellular protein in human umbil ical cord blood-drived mesenchymal stem cells (hUCBMSCs). Methods hUCBMSCs were isolated and cultured by density gradient centrifugation adherence method in vitro. At the serial subcultivation, the hUCBMSCs were randomly divided into 7 groups. In control group, hUCBMSCs were cultured with DMEM medium (containing 15%FBS). In treatment groups, hUCBMSCs were cultured with DMEM medium (containing 15%FBS plusZnSO4•7H2O). The final concentrations of zinc were 0.5, 1.5, 2.5, 3.5, 4.5, and 5.5 mg/L, respectively. The cellular surface antigens of CD29, CD34, CD44, and CD45 at the 3rd generation of hUCBMSCs were detected by flow cytometry. MTT assay was used to detect cell activity of the 3rd generation of hUCBMSCs. The optimum concentration of zinc was selected by the results of MTT as experimental group. The cell growth curves of experimental group and control group were drown by counting cell. The cell surface antigen, reproductive cycle, and DNA content were detected by flow cytometry motheds. The contents of cycl in D2 and CDK4 were detected by Western blot method. Results The positive expression rates of CD29 and CD44 were more than 70% in hUCBMSCs. The cell activity of 2.5 mg/L treatment group was superior to other treatment groups, as experimental group. At 7, 14, and 28 days, the contents of DNA, total cellular protein, cycl in D2, and CDK4 of hUCBMSCs were significantly higher in experimental group than those in control group (P lt; 0.01). The percentage of hUCBMSCs at S stage and prol iferation index in experimental group were also significantly higher than those in control group (P lt; 0.01). Conclusion Zinc (0.5-4.5 mg/L) has the promoting effect on the hUCBMSCs activity, and 2.5 mg/L is the optimal concentration. Zinc (2.5 mg/L) can accelerate the prol iferation and DNA reproduction of hUCBMSCs and increase the contents of cycl in D2 , CDK4, and cellular total protein.