The study was aimed to investigate the expression of COX-2 in bone marrow cells of chronic leukemia patients and its potential pathogenetic implications. Western blot was applied for detecting COX-2 expression levels in bone marrow cells of 67 chronic leukemia patients and beta-actin expression levels. Bone marrow aspirations from 14 healthy donors were used as negative controls. The results showed that the positive rates of COX-2 in chronic-phase group of chronic myeloid leukemia (CML-CP) and in group of chronic lymphocytic leukemia (CLL) were 76.32% (29/38) and 75.86% (22/29) respectively. Both CML-CP and CLL group showed a higher expression than control group (p = 0.0000, p = 0.0000 respectively). The expression of LDH in Cox-2 positive group was higher than that in Cox-2 negative group, and the difference between the two groups was statistically significant (p < 0.001). It is concluded that the expression of COX-2 protein can be detected in bone marrow cells of CML-CP and CLL and the expression level of LDH were higher in cells of CML-CP and CLL. The expression of COX-2 may be correlated with prognosis of CML-CP and CLL.