Objective To investigate the proliferation inhibitory effect and to explore the molecular mechanism of curcumin on pulmonary fibroblasts. Methods Fibroblasts derived from lung tissue of patients with idiopathic pulmonary fibrosis ( IPF) was cultured in vitro and incubated with curcumin at different concentrations for different time. Fibroblasts were randomized into 5 groups, ie. a control group and 4 curcumin groups ( intervened by 5, 10, 20, 40 μmol / L curcumin, respectively) . MTT assay was used to determine the inhibitory rate of curcumin on the proliferation of pulmonary fibroblasts. Apoptosis and the Caspase-3 expression of pulmonary fibroblasts were identified by flow cytometry ( FCM) . Variables were compared with One-Way ANOVA. The correlations between variables were analyzed using Pearson’scorrelation coefficient. Results Curcumin inhibited pulmonary fibroblasts proliferation in a dose-dependent and time-dependent manner( r =0. 886, r = 0. 832, respectively, all P lt; 0. 01) . Apoptosis rate of pulmonary fibroblasts in 4 curcumin groups was ( 29. 58 ±2. 13) % , ( 64. 36 ±3. 92) %, ( 72. 98 ±4. 42) % , ( 83. 14 ±2. 51) % , respectively, which was significantly higher than that in the control group[ ( 3. 84 ±1. 88) % , P lt;0. 01] . The positive expression rate of apoptosis-regulating protein caspase-3 was ( 26. 24 ±3. 64) % ,( 44. 87 ±5. 31) % , ( 57. 44 ±4. 23) % , ( 73. 65 ±5. 01) % , respectively, which was significantly higher than that of the control group[ ( 4. 02 ±0. 62) % , P lt; 0. 01] . Conclusions In vitro, curcumin can significantly inhibit proliferation and induce apoptosis of pulmonary fibroblasts of patients with IPF. The mechanism maybe associated with up-regulating expression of Caspase-3.