In order to explore the probability of PCC-ring (PCC-R) in G,2,/M-PCC cells could be used to quantify the extent of ionizing radiation damage, premature chromosome condensation (PCC) induced by Calyculin A was analyzed. Peripheral blood samples were irradiated with 0, 4, 8, 12, 16 and 20 Gy ,60,Co γ-rays. The PCC-R, which was induced by Calyculin A after culture of 48 h, was observed in the samples exposed to different dose of ,60,Co γ-rays. The G,2,/M-PCC index and the distribution of PCC-R were calculated; the dose-response curves between the frequency of PCC-R and exposed dose level were established. The results showed that PCC was successfully induced by Calyculin A. The G,2,/M-PCC index decreased with exposed dose level. The PCC-R distribution followed a Poisson law for most of dose levels except 20 Gy. The frequency of PCC-R increased with the exposed dose level. And the dose-effect curve between the frequency of hollow-, kidney-shape ring and exposed dose level was fitted with two models, a linear model ,y,=0.0128x−0.0104 ,R,2,=0.9898 and a non-linear model ,y,=0.00002x,2,+0.0085x+0.0011 ,R,2,=0.9996. The frequency of PCC-R in peripheral blood lymphocyte G,2,/M-PCC cells induced by Calyculin A could be used to quantify the extent of ionizing radiation damage.