Abstract: Objective To study the cell death caused by ricin and the cell cycle influenced by ricin.Methods To detect the cell toxicity by MTT and to analyse cell cycle by flow cytometric analysis.Results The ricin of 10-3μmol·L^-1 was enough to cause cell death.The toxicity of cell increased while the concentration of ricin increased.The cell viability was 39.6% after 10μmol·L^-1 ricin treating the HeLa cell for 24 hours.The typical apoptosis was induced by 0.05μmol·L^-1 ricin.The apoptotic cells mainly showed chromatin condensation and disintegration,crescentic nuclear and membrane bound apoptotic bodies formation.Conclusion The ricin of 0.05μmol·L^-1 had no effect on the G₀/G₁ phase of cell cycle,but induced G₂/M.The percentage of G₂/M cells increased from 13.86±0.47% to 33.15±0.45% in 24 hours.