1) Background: Keloids occur after the failure during the wound-healing process, persist the inflammation and are refractory to various treatments. The pathogenesis of keloids is still unclear. We previously analyzed the gene expression profiles in keloid tissue using microarray and Northern blot analysis and found that HtrA1 was markedly upregulated in the keloid lesions. HtrA1 is a member of the HtrA family of serine protease, has been suggested to play a role in the pathogenesis of various diseases including age-related macular degeneration and osteoarthritis by modulating proteins in extracellular matrix or cell surface. We focused on HtrA1, analyzed the localization and the role in keloid pathogenesis. 2) Methods: Twenty seven keloid patients and seven unrelated patients were enrolled in this study. We performed in situ hybridization analysis, immunohistochemical analysis, western blot analysis and cell proliferation assay. 3) Results: First, the fibroblast-like cells expressed HtrA1 higher in the active keloid lesions than in the surrounding lesions in situ hybridization. Second, the proportion of HtrA1-positive cells in keloid was higher than that of in normal skin significantly in immunohistochemical analysis. Third, HtrA1 protein was up-regulated, relative to normal skin tissue samples in western blot analysis. Finally, silencing of HtrA1 gene expression suppressed the cell proliferation significantly. 4) Conclusion: HtrA1 was highly expressed in keloid tissues and the suppression of HtrA1 gene inhibited the proliferation of keloid-derived fibroblasts. HtrA1 may promote keloid development through accelerating cell proliferation and remodeling keloid-specific extracellular matrix or cell surface molecules. HtrA1 is suggested to have an important role in keloid pathogenesis.