Magnesium–calcium (Mg-Ca) alloys have emerged as promising candidates for temporary bio-implant applications due to some notable mechanical, biodegradability and biocompatibility properties. However, the corrosion behavior of Mg-Ca alloy, especially in protein-containing physiological environments, remains insufficiently understood. This study investigates the effect of bovine serum albumin (BSA) addition to Hank's Balanced Salt Solution (HBSS) on the corrosion and stress corrosion cracking (SCC) behavior of Mg-Ca alloy. A combination of potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and surface characterization techniques—optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR)—were employed. The results indicate that BSA adsorption on the alloy surface initially inhibits dissolution, reducing corrosion rates during the first 24 hours. However, prolonged immersion leads to enhanced corrosion, driven by the chelation of BSA with Ca²⁺ ions, which induces cracks in the surface film and promotes alloy dissolution. Furthermore, the fractography reveals that the Mg-Ca alloy is susceptible to SCC in an HBSS environment. However, no evidence of SCC was observed in the HBSS+BSA environment. These findings provide new insights into the complex interactions between proteins and Mg-based implants, contributing to the design of more reliable temporary bio-implant materials.