Abstract： Objective To observe the possible mechanism and inhibitory effects of curcumin on pulmonary fibrosis induced bleomycin in rats at the fibrosing stage. Methods 80 male Sprague-Dawley rats were random divided into 4 groups (20 rats in each group). Rats in the fibrosis model group, the prednisone group and the curcumin group were induced by instilled bleomycin through tracheal, rats in the control group with same volume normal saline. Since the 15th day after bleomycin administration, the curcumin group and prednisone group were given curcumin (300 mg/kg) or prednisone (5mg/kg) per day by intragastric administration, respectively. The normal control group and the model group were given 1% sodium carboxymethyl cellulose ( 10ml/kg). Six rats of each group were random sacrificed on the 21st, 28th, 42nd and 56th days after bleomycin administration. The histological changes of the pulmonary were evaluated by H. E and Masson dyeing. The expressions of transforming growth factor-β1 (TGF-β1), platelet-derived growth factor (PDGF) and hydroxyproline in the tissue of pulmonary were assessed by immunohistochemistry and digestion method. Results Pulmonary fibrosis and hydroxyproline level in the curcumin group were obviously reduced as compared with the model group on the 42nd and 56th day[42 d:1. 28 ±0. 61 vs 2. 28 ±0. 39,P <0. 01 ;(1.73 ±0. 22)mg/g vs (2.50 ±0. 37) mg/g, P <0.01;56 d:1.00 ±0.59 vs 1.73 ±0.36, P< 0. 05; ( 1.57 ± 0. 36) mg/g vs (2. 20 ± 0. 42) mg/g, P < 0. 01 ], and it was also lower than that in prednisone group on the 42nd day( P < 0. 05 ). The expression of TGF-β1 and PDGF in the curcumin group were obviously lower than that in the model group on the 28th, 42nd and 56th day[28 d:TGF-β1 :3642. 05 ±839. 31 vs 5067. 35 ±738. 39, P <0. 05 ;PDGF:2957. 55 ±739. 16 vs 4457. 75 ±568. 39, P <0. 05;42 d: TGF-β1: 2689. 73 ± 529.22 vs 4089. 50 ± 619. 37, P < 0. 01; PDGF: 2834. 46 ± 567. 16 vs 3239. 52 ±628. 26, P <0. 01 ;56 d:TGF-β1: 1968.57 ±408. 36 vs 2968.20 ±498.42, P <0. 01 ;PDGF: 1083.36 ±381.35 vs 2019. 40 ±412. 36, P <0. 01 ], which was lower than that in prednisone group on the 42nd and 56th day (42 d,TGF-β1 :3529. 07 ±981.35,PDGF:2618. 34 ±813. 34;56 d,TGF-β1 :2530. 83 ±439. 37,PDGF: 1738. 35 ±536. 62, Pall <0. 05 ) , and it had no obvious difference compared with control group on the 56th day ( P > 0. 05 ). Conclusion Curcumin could alleviate bleomycin-induced pulmonary fibrosis in rats at the fibrosing stage by inhibiting the expressions of TGF-β1 and PDGF.