Candida albicans (C. albicans) is a common opportunistic fungal pathogen that can cause infections ranging from superficial to severe systemic diseases. This study investigates the antifungal effects of metformin on C. albicans and explores its underlying mechanisms. Growth inhibition was assessed via XTT assays, and hyphal formation and morphological changes were observed by light microscope and scanning electron microscopy (SEM). Mitochondrial membrane potential (MMP) and reactive oxygen species (ROS) levels were measured with JC-1 and DCFH-DA probes, respectively. Gene expression related to ROS and autophagy was quantified by RT-qPCR, and autophagosomes were visualized using transmission electron microscopy (TEM). Metformin significantly inhibited C. albicans growth and hyphal formation, altered cell morphology, reduced MMP, and increased ROS levels. It activated autophagy in planktonic C. albicans but suppressed it in biofilm forms. Additionally, metformin exhibited synergistic effects with amphotericin B against planktonic C. albicans and with caspofungin against biofilms. The findings suggest that metformin exerts antifungal activity by modulating MMP, ROS levels, and autophagy-related pathways, and enhances the efficacy of specific antifungal drugs.