Objective To investigate whether AcSDKP can inhibit collagen synthesis in cultured rat cardiac fibroblasts mediated by transforming growth factor beta1(TGF-βSUB>1/SUB>).Methods Neonatal rat cardiac fibroblasts were isolated. The synthesis of collagen was measured by SUP>3/SUP> Hproline incorporation assay. The expressions of type Ⅰ and Ⅲ collagen protein were detected by immunocytochemistry and Western blotting. Results SUP>3/SUP> Hproline content increased gradually (147.6±10.2， 229.2±16.4，427.0±40.6，454.8±26.1 CPM) and was 1.61， 2.50，4.66 and 4.97 times of control group(91.6±9.8 CPM) respectively in rat cardiac fibroblasts mediated by TGF-βSUB>1/SUB> concentration of 1μg/L, 2.5μg/L, 5μg/L and 7.5μg/L. Compared with TGF-βSUB>1/SUB> group (5μg/L), SUP>3/SUP> Hproline content decreased gradually(378.8±6.4，292.8±14.4，130.6±17.6 and 230.6±19.4 CPM) and was 88.7%, 68.6%， 30.6% and 54.0% of TGF-β1 group with increasing of AcSDKP concentration(10SUP>-10/SUP>mol/L, 5×10SUP>-10/SUP>mol/L, 10SUP>-9/SUP>mol/L, 10SUP>-8/SUP>mol/L). Compared with control group, the expression of collagen type Ⅰ and type Ⅲ in rat cardiac fibroblasts increased significantly in TGF-βSUB>1/SUB> group(5μg/L). Obsorbance values