To investigate the radiation — induced apoptosis of human fibroblasts with different radiosensitivity, the methods of TUNEL and FCM were employed to test the apoptosis of cells treated with ,60,Co ,γ,—rays. The results of experiments indicated that : (1) Surviving fraction experiment identified the No 6 fibroblast cells have a high radiosensitivity than that of No 8 cells after exposured to ,60,Co ,γ,—rays; (2) Apoptosis rate has a positive relationship with radiosensitivity by the methods of TUNEL and FCM, in accordance with the result made by the surviving fraction experiment; (3) Both apoptosis rate and radiosensitivity increased within the 48 hours after radiation. In this conclusion is that : The changing of apoptosis rate can reflect the radiosensitivity level of cell line; the changing of cellular apoptosis rate and radiosensitivity were time—dependant after radiation. it is possible that apoptosis may be an important marker for judging cellular radiosensitivity.