Heat shock protein 27 (Hsp27), a member of the heat shock protein (Hsp) family, is critical in the regulation of cancer development, progression and chemotherapy resistance. However, the role of Hsp27 in the pathogenesis of pediatric acute leukemia (AL) remains unknown. In this study, we evaluated the expression levels of Hsp27 in bone marrow samples from 94 children with newly diagnosed acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML) and 5 leukemia cell lines. Additionally, we transfected a target-specific siRNA duplex against Hsp27 into leukemia cells, and examined the chemosensitivity and cell apoptosis in the response to antitumor drugs. Hsp27 was abundantly expressed in newly diagnosed AML-M4/M5 bone marrow mononuclear cells (BMMCs) and THP-1, OCI/AML-3 leukemia cell lines. Furthermore, its expression was positively correlated with the clinical status in pediatric M4/M5 subtypes. Knockdown of Hsp27 expression increased the chemosensitivity of leukemia cells and the anticancer drug-induced apoptosis. These results support the theory that Hsp27 plays a contributory role in the pathogenesis of pediatric AML-M4/M5. Therefore, Hsp27 may be exploited as a new target for enhancing the efficacy of chemotherapeutic drugs against leukemia.