Abstract： Objective To explore the p27 gene expression and clinical significance in acute leukemia (AL).Methods RT-PCR was used for testing the mRNA levels of p27 gene in bone marrow mononuclear cell of 65 cases of newly diagnosed AL patients and 41 controls.The correlation between the p27 gene expression positive rate and age, sex, peripheral blood white blood cell count and extramedullary infiltration were analyzed simultaneously in AL patients.Results The positive rate of p27 gene expression (36.9 ％,24/65)was significantly lower in AL group than that in the control group (87.8 ％,36/41) (P ＜0.05),and which was lower than the control group (P ＜0.05) in the AML group (34.2 ％,13/38) and the ALL group (37.5 ％,9/24).However,comparing AML group with ALL group,the difference was not statistically significant (P ＞0.05).At the same time,compared the p27 gene expression positive rate of ≥ 14 years old group (52 cases) and ＜14 years old group (13 cases),and also compared in male group (34 cases) and in female group (31 cases),there was no statistically difference (P ＞0.05); Compared the p27 gene expression positive rate of peripheral blood white blood cell count ≥20×109/L group (31 cases) and ＜20×109/L group (34 cases),also compared with in extramedullary infiltration group (37 cases) and in no extramedullary infiltration group (28 cases),the relationship of p27 gene expression positive rate with peripheral blood white blood cell count as well as extramedullary infiltration was a negative correlation (r =-0.284,P ＜ 0.05,r =-0.300,P ＜ 0.05).Conclusion There is p27 mRNA expression deletion in AL patients,and the deletion is present in the AML and ALL at the same time.p27 mRNA expression is negatively correlated with peripheral blood white blood cell count or extramedullary infiltration,which might be one of the mechanisms of occurrence and development of AL.