Previous studies have shown an anticancer effect of vitamin D, but the mechanisms underlying this action have not been fully explored. Here we show that 1,25-dihydroxyvitamin D3 (VD3, the active form of vitamin D) significantly promoted apoptosis in the undifferentiated gastric cancer cell line HGC-27, and this was accompanied by a concurrent increase in phos-phatase and tensin homolog deleted on chromosome 10 (PTEN) expression on VD3 treatment.