Objective: To explore the correlation between Candida albicans and the development of oral leukoplakia (OLK), and to provide a basis for improving the pathogenic mechanism of the malignant transformation of OLK. Methods: Oral microbiome data were obtained from public databases (NCBI BioProject, PRJNA788378; GEO, GSE227919), and bioinformatic methods were employed to evaluate the correlation between Candida albicans infection and OLK. Approval was obtained from the institutional Medical Ethics Committee. A tissue microarray was constructed using samples collected from an OLK clinical cohort. Hematoxylin and eosin (H&E) staining and periodic acid-Schiff (PAS) staining were performed to analyze the relationship between the Candida albicans detection rate and clinicopathological features. Approval was obtained from the institutional Animal Ethics Committee. A mouse model was established by combining 4-nitroquinoline-1-oxide (4NQO) in drinking water with oral inoculation of Candida albicans (4NQO + Candida albicans group), while mice treated with 4NQO in drinking water and PBS served as the control group (4NQO + PBS group). The degree of epithelial dysplasia was compared between the two groups to assess the impact of Candida albicans infection on lesion progression (defined in this study as the progression from mild/moderate epithelial dysplasia to severe dysplasia/carcinoma in situ or invasive squamous cell carcinoma). Results: Bioinformatic analysis revealed that the detection rate of Candida albicans in OPMDs and OLK tissues was significantly higher than that in the healthy control group. Staining results of clinical samples demonstrated that Candida albicans colonized OLK lesions; compared with Candida albicans-negative patients, positive patients exhibited a state of high-grade progression. Animal experiments indicated that, compared with the 4NQO + PBS group, the degree of oral epithelial dysplasia in the 4NQO + Candida albicans group was significantly exacerbated, and the malignant transformation rate was higher, suggesting that Candida albicans promotes the high-grade progression of OLK. Conclusion Candida albicans exhibits a increasing trend during the malignant progression of the OLK. It aggravates the degree of epithelial dysplasia in OLK and promotes its transformation into high-grade lesions, suggesting that Candida albicans plays a crucial promoting role in the high-grade progression of OLK.