Background: Over-expression of anti-apoptotic proteins such as Bcl-2 and Mcl-1 is associated with resistance to chemotherapeutic agents such as fludarabine. Moreover, an inverse relationship between miRNA-15a levels with Bcl-2 and Mcl-1 expression has been observed in CLL patients. In this study, the effect of miRNA-15a on apoptosis and sensitivity of the CLL cells to fludarabine was investigated. Methods: After treatments, the Mcl-1 and Bcl-2 expression levels were quantified by RT-qPCR. Trypan blue assay was used to explore the effects of miRNA-15a and fludarabine on cell proliferation. The cytotoxicity was measured using MTT assay and combination index analysis. Cell death was determined using cell death detection ELISA assay and caspase-3 activity assay Kits. Results: Results showed that miRNA-15a clearly decreased the mRNA levels of Bcl-2 and Mcl-1 in a time dependent manner, which led to CLL-II cell proliferation inhibition and enhancement of apoptosis (p < 0.05, relative to control). Transfection of the miRNA-15a synergistically reduced the cell survival rate and lowered the IC 50 value of fludarabine. Furthermore, miRNA-15a significantly enhanced the apoptotic effect of fludarabine. Conclusions: Our data propose that suppression of Bcl-2 and Mcl-1 by miRNA-15a can effectively inhibit the cell proliferation and sensitize CLL cells to fludarabine. Therefore, miRNA-15a can be considered as a potential therapeutic target in CLL resistant patients.