<p>Biodegradable polymer coatings are commonly used as protective barriers on magnesium (Mg) and its alloys. The properties of polymers, such as crystallinity and degradation properties, have a crucial impact on their corrosion resistance. In this work, polyhydroxybutyrate (PHB) coatings are deposited on Mg sheets with a thickness similar to that of cardiovascular stents to assess the degradation behavior, and poly-lactic acid (PLA)-coated Mg is also investigated to compare the structure–property-performance relationship. The hydrogen evolution volume (HEV) of the PHB-coated sample decreases by 30% after immersion in artificial blood plasma (AP) for 7&#xa0;days, whereas the PLA-coated sample shows an increase of 154%. The PHB coating also shows excellent durability at a constant voltage, compared to severe rupture of the PLA coating. The degradation behavior of the coated-Mg samples is evaluated in AP solution containing different concentrations of the bovine serum albumin (BSA). Corrosion is inhibited as the protein concentration increases. The degradation rates of the Mg, PLA-coated Mg, and PHB-coated Mg decrease by 65%, 88%, and 75% for 5&#xa0;g L⁻¹ BSA, respectively. Our results reveal that higher crystallinity and less acidic degradation products give rise to better durability, while the acid self-catalytic effect leads to the failure of PLA. The protein-polymer interactions are determined and the empirical relationship of HEV is established.</p> Graphical Abstract <p></p>