Chronic lymphocytic leukemia (CLL) is a common leukemia in adults, but its pathogenesis is still poorly understood. Recently, extensive evidence suggests that the malignant cells of CLL patients secrete a range of cytoprotective cytokines including interleukin-4 (IL-4). IL-4 induced the rapid phosphorylation(p) and activation of the signal transducer and activator of transcription (STAT)-6 transcription factor in CLL cells in vitro. Interleukin-9 (IL-9) is not expressed by Th2 and Th9 cells in the absence of STAT6 expression. To elucidate whether there was a function link between IL-9 and STAT6 in CLL, MEC-1 cells were analyzed using RT-PCR, and western blot. Interestingly, when added with recombinant human IL-4 (rIL-4) in culturing MEC-1 cells, expressions of p-STAT6 and IL-9 in MEC-1 cells increased at a time-dependent manner and their expressions could be inhibited by STAT6 inhibitor. Our data indicated that the upregulation of IL-9 induced by pSTAT6 may be involved in the pathogenesis of CLL.