Aim To explore the potential mechanism of metformin on ATP-binding cassette transport A1 (ABCA1) expression. Methods J774A.1 macrophages were treated with metformin and cycloheximide, and ABCA1 expression was determined by Western blot. His-tagged ABCA1 and HA-tagged Ub plasmids were co-transferred into HEK293 cells and stimulated with metformin. Co-immunoprecipitation (Co-IP) was used to test the binding ability of ABCA1 and ubiquitin. Candidate E3 ubiquitin-protein ligases (CE3) of ABCA1 were identified through Co-IP-based proteomics. The MIB1 plasmid was constructed and transferred into HEK293 cells, and Western blot was used to determine the effect of metformin and MIB1 on ABCA1 expression. Results Metformin increased the expression of ABCA1 in J774A.1 cells (P＜0.01), and inhibited ABCA1 degradation (P＜0.05). Metformin disrupted the binding of ABCA1 to ubiquitin (P＜0.05). The proteins regulated by metformin in ABCA1 expression were primarily enriched in pathways related to cell development, inflammation and immune defense. Metformin may upregulate ABCA1 protein expression via MIB1 (P＜0.05). Conclusion Metformin inhibits the degradation of ABCA1 by blocking the ubiquitin-proteasome system (UPS), and MIB1 might act as a candidate E3 ubiquitin-protein ligase (CE3) for ABCA1.