Objectives: Hedyotis diffusa is used to treat cancer in traditional Korea Medicine. So this study was carried out to examine the expression of cell cycle related genes in HL-60 cells undergoing apoptosis by the methanol extract of Hedyotis diffusa. Methods: 1. HL-60 cells were treated with various concentrations (from 200 to $50{mu}g/ml$)of methanol extract and H20 extract ($200{mu}g/ml$) of hedyotis diffusa. After 48 h later, the cells were tested for viability by MTT assay. 2. The HL-60 cells were treated with $200{mu}g/ml$ of methanol extract for the indicated periods. The whole cell lysates were prepared and analyzed by western blotting using anti-p53 antibody. 3. The nuclear extract were prepared and analyzed by western blotting using anti-p21 antibody, anti-p27 antibody, anti-cyclin A antibody, anti-cyclin E antibody and anti-CDK2 antibody. Results: 1. The methanol extract of Hedyotis diffusa induced the death of HL-60 cells in a dose dependent manner. 2. The methanol extract of Hedyotis diffusa makedly decreased the level of p21/Cipl and cyclin A in a time dependent manner. 3. The methanol extract of Hedyotis diffusa markedly increased the level of p27/Kipl and cyclin E in a time dependent manner. 4. The methanol extract of Hedyotis diffusa markedly did not affect the level of CDK2. Conclusions: These results provide evidence that expression of cell cycle related genes in HL-60 cells undergoing apoptosis by the methanol extract of Hedyotis diffusa mainly results from decreased level of p21/Cipl and increased level of p27/Kipl of the cell cycle related genes.