To evaluate the expression of cyclin dependent kinase inhibitor P27(Kip1) in leukemia and to investigate its clinical significance, the P27(Kip1) protein in bone marrow or peripheral blood samples from 82 cases of leukemia was measured by Western blot and enhanced chemoluminescence (ECL). The results showed that the expression of P27(Kip1) protein in ALL was higher than that in ANLL (P = 0.033) and also that in CML (P = 0.008). P27(Kip1) expression in CLL was higher than that in CML too (P = 0.017). In acute leukemia, the effective rate (CR and PR) of initial chemical therapy in the group of P27(Kip1) > 0.655 was higher than that in the group of P27(Kip1) < or = 0.655, P = 0.041. For ANLL and ALL patients, the survival time in the group of P27(Kip1) > 0.655 was longer than that in the group of P27(Kip1) < or = 0.655, P = 0.0065. There were similar statistical significance for ANLL and ALL patients, P = 0.0271 and P = 0.0266 respectively. There was a negative correlation between chromosomal abnormalities and P27(Kip1) expression in ALL patients (r = -0.775, P = 0.04). The expression of P27(Kip1) protein appeared nothing to do with sex, age, white blood cell number, blast cell number in peripheral blood, serum LDH or uric acid. In conclusion, the expression level of P27(Kip1) protein is in relation to the effect of initial chemical therapy and survival time, so that the lower P27(Kip1) expression may associated with poor prognosis in acute leukemia.