This study was purposed to investigate the ratio of Th17 cells and CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells in peripheral blood of patients with chronic lymphocytic leukemia (CLL) and to explore their roles in the pathogenesis and clinical diagnosis. Based on the number of peripheral lymphocytes and treatment condition, the CLL patients were divided into 2 groups: untreated group (n = 30) and remission group (n = 15), the healthy control group (n = 20) was set up as well. The frequencies of Th17 and Treg cells of all cases were detected by flow cytometry (FCM). The results showed that frequencies of CD3(+)CD4(+)T cells and Th17 cells were significantly higher in untreated group than that in healthy control group (P < 0.05), the frequencies of CD3(+)CD8(+)T cells and Treg cells were significantly lower in untreated group than that in healthy control group (P < 0.05), the ratio of Th17/Treg was significantly higher in untreated group than that in healthy control group (P < 0.05). The frequencies of Th17 were not statistically different between remission and healthy control groups, the frequencies of Treg cells were significantly lower in remission group than that in healthy control group (P < 0.05), the ratio of Th17/Treg was significantly higher in remission group than that in healthy control group (P < 0.05), frequencies of Th17 cells were markedly lower in remission group than that in untreated group (P < 0.05). It is concluded that Th17/Treg imbalance exists in patients with CLL, which may play a key role in pathogenesis and development of CLL.