Abstract: The morphologies, microstructure and composition distribution of magnesium alloy anodic materials for seawater batteries were studied by metallographic microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The corrosion behavior and electrochemical properties of the Mg alloys were also investigated by the constant current method, potential polarization and collecting gas through drainage. The results showed that tin restrained β-Mg₁₇Al₁₂ phase precipi-tation along grain boundaries. With the content of tin increasing, granular Mg₂Sn phase improved. After uniform heat treatment, most of β-Mg₁₇Al₁₂ phase dissolved, but most of Mg₂Sn phase did not. Tin could improve the self-corrosion potential and the release hydrogen rate. The magnesium alloy anode with 1% tin had high discharge potential and current efficiency. With the current density increasing, the release hydrogen rate augmented. The current efficiency reached 82.28% at 20mA·cm^-2. The main compositions of the corrosion products were MgO and Al₂O₃ which were easily peeled off. As a result, more negative and stable work potential was produced and the reaction was accelerated continuously.