Objective　To investigate the inhibitory effects of sTβRⅡ on Smad signal induced by TGF-β1 in neonatal rat cardiac fibroblasts and myofibroblast differentiation.  Methods　Cardiac fibroblasts obtained from neonatal rats were cultured and randomly divided into 4 groups: PBS control group, TGF-β1 (5 ng/ml) group, sTβRⅡ (50 ng/ml) group and TGF-β1+sTβRⅡ group. 30min, 1h and 2h after the treatment, the expression of P-Smad2 and Smad3 was measured by immunocytochemistry (ICC) staining; after 24h, the expression of  α-SMA was measured by ICC staining.   Results　Compared with that of PBS control group, the expression of P-Smad2, Smad3 (percentage of nuclear stained cells) and α-SMA increased significantly in TGF-β1 group (P＜0.05); compared with that of TGF-β1 group, the expression of P-Smad2, Smad3 (percentage of nuclear stained cells) and α-SMA decreased markedly in TGF-β1+sTβRⅡ group (P＜0.05).  Conclusions　sT RβⅡ antagonizes the phosphorylation and nuclear translocation of Smad2/Smad3 protein induced by TGF-β1, blocks Smad signal transduction pathway, and inhibits myofibroblast differentiation in neonatal rat cardiac fibroblasts.