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Metal ions perform a wide variety of functions associated with life processes. In this work, we investigated the influence of Mg2+ on the denaturation and aggregation of bovine serum albumin (BSA) during heat treatment. The unfolding and denaturation of proteins during food processing, especially heat treatment, has a major influence on their functional properties. Our results show that Mg2+ significantly stabilized the secondary structure of BSA when the protein was heated at 80 °C, preventing the transformation of α-helices into unfolded structures. Mg2+ also inhibited the aggregation of BSA into larger, heterogeneous structures. Moreover, after adding Mg2+, the melting temperature of BSA increased from 70.20 °C to 73.74 °C, further indicating that Mg2+ has a stabilizing effect. Finally, molecular dynamics (MD) simulations revealed that Mg2+ preferentially binds multivalently to the carboxylate groups of Asp and Glu BSA residues, and the observed stabilizing effect could be attributed to the crosslinking of secondary structure elements within BSA induced by Mg2+ binding. Considering the ubiquity of Mg2+, our work provides a facile strategy to control BSA unfolding and aggregation, which is helpful for enhancing the processing and storage properties of BSA or other proteins during food processing.