The microstructural characterization, corrosion behavior and tensile properties of the extruded lean Mg-1Bi-0.5Sn-0.5In (wt.%) alloy were investigated through scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray photoelectron spectroscopy (XPS), electrochemical measurements and tensile tests. The results reveal that a microstructure consisting of dynamically recrystallized and deformed grains is obtained. Notably, the investigated alloy exhibits excellent strength-ductility synergy, with tensile yield strength (TYS), ultimate tensile strength (UTS) and elongation (EL) of 254.8 MPa, 315.4 MPa, and 25.3%, respectively. Furthermore, in 3.5 wt.% NaCl solution, with the increase of immersion time, the dominant corrosion mechanism of the studied alloy transforms from pitting corrosion to filiform corrosion. After the immersion for 24 h, a composite oxide film (SnO₂- Bi₂O₃-In₂O₃) is formed, which delays the corrosion process, and the corrosion rate (P_H=1.53 mm/a) is finally stabilized.