Abstract: Objective To investigate the effects of Thalidomide（THD）on transdifferentiation of human fetal lung fibroblast (HFL-F) to myofibroblast (MF) induced by Transforming Growth Factor-β1 (TGF-β1) and on differentiated MF. Methods HFL-F to MF differentiation was induced with 5μg/L TGF-β1. The effect of 50μg/L THD on HFL-F to MF transdifferentiation was evaluated by measuring hydroxyproline (Hyp) content with alkaline hydrolysis method, α-smooth muscle actin (α-SMA) protein with Western Blot, α-SMA and collagen Ⅲ (COL Ⅲ) mRNA with semiquantitative RT-PCR. Results THD could inhibit TGF-β1 induced up-regulation of Hyp and COL Ⅲ mRNA expressions (all p<0.05), α-SMA protein synthesis may reduced, but had no effect on α-SMA mRNA expression (p>0.05). For HFL-F treated with 5μg/L TGF-β1 for 96h, THD could inhibit COL Ⅲ mRNA expression (p<0.05). Conclusions TGF-β1 could induce HFL-F to MF transdifferentiation; THD could affect this process by inhibiting Hyp production, α-SMA protein synthesis and COL Ⅲ mRNA expression. THD could additionally inhibit COL Ⅲ mRNA expression in transdifferentiated MF.