Background: Obesity is a known risk and exacerbation factor for bronchial asthma. Leptin is an adipokine secreted by adipocytes and enhances energy consumption. Earlier studies have shown that leptin also activates inflammatory cells and structural cells, including airway epithelial cells, thereby exacerbating inflammation. However, little is known about leptin's effect on normal human lung fibroblasts (NHLFs), which are deeply involved in airway remodeling in asthma. This study aimed to elucidate the direct effect of leptin on NHLFs. Methods: NHLFs were co-cultured with leptin, and production of cytokines/chemokines was analyzed with real-time PCR and cytometric bead arrays (CBA). Expression of alpha smooth muscle actin (α-SMA) in the lysate of NHLFs stimulated with leptin was assessed by western blotting. Expression of leptin receptor (Ob-R) was analyzed by real-time PCR and flow cytometry. NHLFs were transfected with Ob-R small interference ribonucleic acid (siRNA) by electroporation and used for experiments. Results: Leptin enhanced production of CCL11/Eotaxin, monocyte chemoattractant protein-1 (CCL2/MCP-1), CXCL8/IL-8, interferon gamma-induced protein 10 (CXCL10/IP-10) and IL-6 by NHLFs at both the protein and messenger ribonucleic acid (mRNA) levels. Leptin also slightly, but significantly, elevated expression of α-SMA. We found robust Ob-R expression on cell surfaces, and transfection with Ob-R siRNA suppressed the enhanced production of CCL11/Eotaxin, CXCL10/IP-10 and IL-6 by leptin, although not completely. Conclusions: These findings indicate that leptin may contribute to worsening of asthma in obese patients by enhancing production of inflammatory mediators by binding to Ob-R and accelerating myofibroblast differentiation. Keywords: Asthma, Fibroblasts, Leptin, Leptin receptor, Obesity