Background: Hyperglycaemia promotes the proliferation of cardiac fibroblasts (CFs) and collagen synthesis in CFs. However, the molecular mechanism underlying the effects of HG on proliferation and collagen synthesis of CF, is not completely understood. Objectives: The objectives of the present study were to determine whether the STAT proteins has a functional role in high glucose-induced proliferation of CFs and collagen synthesis in vitro and whether the STAT signaling pathway and MAPK signaling pathway have synergetical effects on high glucose-mediated cardiac fibroblasts proliferation and collagen synthesis. Methods: Rat CFs were cultured in Dulbecco's modified Eagle's medium, supplemented with 5.5 or 25 mmol/L D-glucose, in the presence of absence of STAT1 inhibitor Fludarabine, STAT3 inhibitor S31-201 and ERK1/2 inhibitor PD98059. Proliferation were measured by the 3-(4,5-dimethyl-2 thiazoyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, the production of Type I and III collagen was evaluated using real-time quantitative RT-PCR and ELISA, and the phosphorylation expression of STAT1 and STAT3 were analyzed by Western blot. Results: High glucose treatment promoted the proliferation of cardiac fibroblasts and collagen types I and III synthesis. High glucose treatment induced STAT1 and STAT3 phosphorylation in cardiac fibroblasts, the mode and level of STAT1 and STAT3 phosphorylation were significantly different. Fludarabine and S31-201 could both inhibited high glucose stimulated proliferation of cardiac fibroblasts and collagen types I and III synthesis with different effects. Combination of Fludarabine and PD98059 or combination of S31-201 and PD98059 both exhibited stronger inhibitions on proliferation of cardiac fibroblasts and collagen types I synthesis, but the effects and functional modes are different. Conclusion: Both STAT1 and STAT3 mediate the proliferation of cardiac fibroblasts and collagen synthesis induced by high glucose. STAT1 and STAT3 both have synergetic effects with ERK1/2 on regulating proliferation of cardiac fibroblasts and collagen types I synthesis