Disordered differentiation of tendon stem cells (TSCs) during repair of injured tendon can result in the pathogenesis of chronic tendinopathy. Understanding tenocyte differentiation may provide new therapeutic insights for the prevention and treatment of chronic tendinopathy. The aim of our study was to determine if CTGF exerts a similar effect on BMP12-driven differentiation of rat TSCs. In overexpressing and RNA interference CTGF TSCs, tenogenic differentitation and the expression of related genes were determined by immunofluorescence staining, quantitative PCR, and western blotting, with or without BMP12 treatment. The interaction in vitro between CTGF and BMP12 was detected by Chemical crosslinking assay. Our results showed that BMP12 effectively increased the expression of the tenocyte lineage markers scleraxis (Scx) and tenomodulin (Tnmd) at both mRNA and protein levels. Over-expression of CTGF from a lentiviral vector increased the expression of Scx and Tnmd as well as tendon proteins type I collagen (ColI) and tenascin-C (Tn-C) in TSCs compared to non-treated control cells with or without simultaneous BMP12 stimulation. Knockdown of CTGF expression decreased the expression of Scx, Tnmd, ColI and Tn-C compared to control cells. Chemical crosslinking experiments demonstrated a direct interaction between CTGF and BMP12. In conclusion, BMP12 plays a crucial role in tenogenesis via the Smad1/5/8 pathway, and CTGF positively promotes this effect.