Previous studies have found that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3 or VD3] exerts many biological effects, including the inhibition of cell proliferation and induction of apoptosis, but its mechanism of action remains unclear. The goal of our investigation was to explore the effects of 1,25(OH)2D3 on the proliferation of cultured human mesangial cells and their expression of Ki67 in vitro, and to establish its mechanism of action. Cultured human mesangial cells were randomly divided into the following four groups: normal control (N group; administered Dulbecco’s modified Eagle’s medium containing 5% fetal bovine serum), proliferation [epidermal growth factor (EGF) group; administered 10 μg/L EGF], VD3 intervention [administered 10-8 M 1,25(OH)2D3], and proliferation and intervention [EGF+VD3 group; administered 10 μg/L EGF and 10-8 M 1,25(OH)2D3]. Cells were incubated for 48 h with the corresponding treatment, and fluorescence immunocytochemistry and reverse transcription-quantitative polymerase chain reaction were used to detect expression of Ki67 protein and mRNA, respectively. Compared to the N group, Ki67 levels were found to be higher in the EGF group but significantly lower in the VD3 intervention group. Moreover, expression of Ki67 by cells in the EGF+VD3 group was significantly lower than that of those in the EGF group. All of these differences were statistically significant (P < 0.05). In conclusion, 1,25(OH)2D3 inhibited Ki67 expression and the proliferation of human mesangial cells; therefore, Ki67 may be regarded as a potent therapeutic target in mesangial proliferative glomerulonephritis.