This study was aimed to investigate the expression level of murine double minute 4 (MDM4) mRNA in chronic lymphocytic leukemia (CLL) and its prognostic value in CLL. By means of β-actin as internal reference, the real-time quantitative RT-PCR was set up. The expression of MDM4 mRNA in 66 CLL patients was measured by fluorescence dye SYBR Green I. The dispersion of MDM4 expression ratio of groups with different prognostic factors was described by using Mann-Whitney U test. The results showed that the median MDM4 mRNA expression level was 0.037098 (0.088245-0.014875) in CLL patients. The expression level of MDM4 mRNA was significantly higher in patients with P53 gene deletion than that in patients without P53 gene deletion (0.13167 vs 0.030927) (p < 0.001), and also significantly higher in patients with P53 mutation than that in patients without P53 mutation (0.13167 vs 0.03077) (p < 0.001). MDM4 expression was also associated with Binet stages (p = 0.044) and ATM gene deletion (p = 0.046), but was not associated with LDH (p = 0.216), β(2)-MG (p = 0.314), TK1 (p = 0.300), ZAP-70 (p = 0.559), CD38 (p = 0.513) and IgVH mutation status (p = 0.333). It is concluded that the expression level of MDM4 is significantly higher in patients with P53 deletion or mutation. MDM4 expression is significantly associated with Binet stages and ATM gene deletion. MDM4 may be an important prognostic factor in CLL.