Background: Invasive growth of fibroblast cells, which is regulated by multiple biological factors, is the key event in the pathophysiology of keloid scars. Recent studies have suggested that botulinum toxin type A (BoNT-A) could inhibit invasive growth of keloids. However, the molecular mechanisms are unknown. Objective: The authors explore the effect of BoNT-A on the expression of genes relevant to invasive growth in keloid fibroblasts. Methods: With 112 genes that were relevant to invasive growth, the authors utilized microarray analysis to study messenger RNA expression profiles in keloid fibroblasts treated with BoNT-A. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to confirm the microarray results. Results: Analyses from microarray and qRT-PCR revealed that the S100A4 gene was upregulated and that the TGF-beta 1, VEGF, MMP-1, and PDGFA genes were downregulated in fibroblasts treated with BoNT-A. Conclusions: The BoNT-A altered expression levels of S100A4, TGF-beta 1, VEGF, MMP-1, and PDGFA genes in keloid fibroblasts provide a useful clue for exploring the function of BoNT-A and finding a novel treatment for keloid scarring.