Objective To explore the effect of emodin on the proliferation, differentiation into myofibroblasts and collagen synthesis of pulmonary fibroblasts and the underlying mechanisms. Methods Human pulmonary fibroblasts MRC-5 were cultured in vitro, then the cells were inoculated with dimethyl sulfoxide (DMSO) added with 0, 10, 20, 40, 80 and 160 μmol/L emodin for 24, 48 and 72 hours. Inhibitory rate of cell proliferation was analyzed by MTT assay. Based on the results of cell proliferation experiment, MRC-5 cells were treated with DMSO (control group) and 40, 80 μmol/L emodin (in DMSO) for 48 hours. Fluorescence real-time quantitative PCR was then used to measure the mRNA expressions of α-smooth muscle actin (α-SMA), transforming growth factor-β1 (TGF-β1), a disintegrin-like and metalloproteinase with thrombospondin type 1 motif (ADAMTS-1), collagen type 1 (Col1) and collagen type 3 (Col3). The protein expressions of the above mentioned factors were also measured by Western blotting. Results In a concentration- and time-dependent manner, emodin inhibited MRC-5 cell proliferation. After 48 hours of co-culture, in comparison with control group, the mRNA and protein expression levels of α-SMA, TGF-β1, Col1 and Col3 significantly decreased, while the mRNA and protein expression levels of ADAMTS-1 significantly increased in 40 and 80 μmol/L emodin-treated groups. Moreover, in comparison with 40 μmol/L emodin-treated group, the mRNA and protein expressions of α-SMA, TGF-β1, Col1 and Col3 were significantly downregulated, but ADAMTS-1 mRNA and protein expressions were significantly upregulated in 80 μmol/L emodin-treated group. Conclusion Emodin can block pulmonary fibroblast proliferation and differentiation into myofibroblasts, and reduce the synthesis of Col1 and Col3 by inhibiting TGF-β1/ADAMTS-1 signaling pathway.