Moyamoya disease (MMD) is a rare, chronic, and progressive cerebrovascular disorder with unclear underlying causes and mechanisms. Previous studies suggest a potential involvement of endothelial-mesenchymal transition (EndMT) in the pathogenesis of MMD. This study aimed to explore the contribution of EndMT-related genes (ERGs) in MMD. Two datasets, GSE141022 and GSE157628, were integrated as the training set after batch effects removal. Differentially expressed ERGs were identified between MMD and control groups. Functional enrichment analysis and immune infiltration analysis were further performed. LASSO regression was used for hub MMD-related ERG selection. Consensus clustering was used for MMD subtype classification based on these hub MMD-related ERGs. Molecular characteristics between MMD subtypes were analyzed using WGCNA. PPI network was used to illuminate the genetic relationship. The hub MMD-related ERGs were validated in an independent testing set, GSE189993. The nomogram model was constructed and evaluated using ROC curves and calibration plots. Additionally, CCK-8, EdU, wound healing, and western blot were performed to confirm the function of the hub MMD-related ERGs. A total of 107 DE-ERGs were identified. Functional enrichment analysis showed these genes were associated with EndMT and immune response. The infiltrating levels of immune cells were commonly higher in the MMD group. LASSO regression identified 12 hub MMD-related ERGs, leading to the identification of two MMD subtypes. Four ERGs emerged as the final hub MMD-related ERGs after validation in the testing set, including CCL21, CEBPA, KRT18, and TNFRSF11A. The nomogram model exhibited excellent discrimination ability. In vitro experiments showed that CCL21, CEBPA, KRT18, and TNFRSF11A could promote proliferation, migration, and EndMT. This study investigated the potential role of EndMT in MMD and identified four hub MMD-related ERGs, providing potential therapeutic targets for MMD treatment.