The purposes of this study were to determine whether berberine has any effect on phenotype changes and extracellular matrix (ECM) production in nasal polyp-derived fibroblasts (NPDFs) and to investigate the underlying molecular mechanism. NPDFs were pre-treated with berberine prior to induction by transforming growth factor (TGF)-β1. The expression of α-smooth muscle actin (SMA) and collagen type I mRNA was determined by a reverse transcription-polymerase chain reaction, and the expression of α-SMA protein and collagen type I was determined by western blotting and/or immunofluorescent staining. The total soluble collagen production was analysed by the SirCol collagen assay. The expression of several signaling molecules of the TGF-β1 pathway was evaluated by western blot analysis. In TGF-β1-induced NPDFs, berberine significantly inhibited the expression of α-SMA and collagen type I mRNA and reduced α-SMA and collagen protein levels. Berberine only suppressed the expression of pp38 among the evaluated signaling molecules. SB203580 (a specific inhibitor of p38 kinase) markedly suppressed the increased expression of collagen type I and α-SMA in TGF-β1-induced NPDFs. Berberine exerts suppressive effects on phenotype changes and ECM production in NPDFs via p38 signaling pathway interference. The findings provide new therapeutic options for ECM production in nasal polyps. Copyright © 2012 John Wiley & Sons, Ltd.