The expression of heat shock protein 70 (Hsp70) is induced in response to many factors including high temperature, infection, metal pollutants and toxic chemicals. In this study, Megalobrama amblycephala HSP70 promoter was cloned, and characteristic heat shock elements (HSEs) were identified in the promoter region. The recombinant M. amblycephala Hsp70 protein (rMaHsp70) was expressed and purified from Escherichia coli BL21 (DE3). To evaluate in vivo immune response of rMaHsp70, we administered intraperitoneal (IP) injection, and demonstrated that rMaHsp70 stimulated M. amblycephala immune activity by inducing the expression of HSP70, HIF-1α, HSC70, CXCR4b, TNF-α and IL-1β mRNAs in liver, headkidney, spleen and gill, as well as SOD, glutathione, lysozyme and interferon alpha proteins in serum and liver. The effect of rMaHsp70 as adjuvant against Aeromonas hydrophila was assessed by injecting a mixed vaccine of rMaHsp70 and A. hydrophila (A. hydrophila/Hsp70) into M. amblycephala, and the relative percent survival (RPS) in the A. hydrophila/Hsp70 group was 75% compared to 50% in the A. hydrophila/PBS group. Furthermore, rMaHsp70 also promoted the proliferation and suppressed apoptosis in M. amblycephala fin cells (MAF) in a dose-dependent manner. Taken together, these results suggest that rMaHsp70 can induce organic immune response and improve environmental tolerance.