Background <p>Mitochondrial dysfunction is closely associated with cancer development. Colorectal cancer (CRC) cells often exhibit altered energy metabolism, characterized by increased glycolysis and reduced oxidative phosphorylation. Enhancing mitochondrial biogenesis and function may represent a promising therapeutic approach. High-dose vitamin C has demonstrated anti-tumor properties and the ability to reverse the Warburg effect, but its role in regulating mitochondrial biogenesis and function remains unclear.</p> Methods <p>We evaluated the altered mitochondrial functional status of HCT116 colorectal cancer cells compared to FHC colorectal epithelial cells, assessed the effects of high-dose vitamin C on mitochondrial biogenesis and function in HCT116 cells, and explored the underlying regulatory mechanisms.</p> Results <p>HCT116 cells exhibited mitochondrial dysfunction compared to FHC cells, including decreased expression of electron transport chain complexes III and IV, reduced TFAM levels, and lower mtDNA content. Vitamin C treatment significantly enhanced mitochondrial biogenesis and function, as reflected by increased AMPK phosphorylation, upregulation of PGC-1α, SOD2, NRF2, TFAM, MT-CYB, and MTCO1, elevated mtDNA content, restored membrane potential, enhanced oxidative phosphorylation, and reduced glycolytic activity. Furthermore, vitamin C markedly suppressed HCT116 cell viability and clonogenic capacity, while these effects were substantially diminished by cotreatment with Compound C.</p> Conclusion <p>This study demonstrates that high-dose vitamin C ameliorates mitochondrial dysfunction and promotes mitochondrial biogenesis and function in colorectal cancer cells through activation of the AMPK–PGC-1α signaling pathway, thereby suppressing tumor cell proliferation. These findings suggest that vitamin C may serve as a promising therapeutic agent for targeting mitochondrial metabolism in colorectal cancer.</p>