The proliferation and differentiation of cardiac fibroblasts (CFs) is central to cardiac fibrosis. Betulinic acid (BA) is an active compound isolated from the bark of the birch tree Betula spp. (Betulaceae) and has been shown to attenuate hepatic fibrosis. However, the effect of BA on the high glucose‑induced fibrosis response in CFs remains to be elucidated, therefore, the present study investigated the effect of BA on high glucose‑induced CFs and examined the possible mechanism underlying the effect of BA on CF transdifferentiation. CFs were pre‑incubated with various concentrations of BA for 24 h and then stimulated with high glucose (25 mM) for various times. Cell proliferation was evaluated using an MTT assay. The mRNA expression levels of α‑smooth muscle actin (SMA) and transforming growth factor (TGF)‑β1 were determined using reverse transcription‑quantitative polymerase chain reaction analysis. The protein expression levels of α‑SMA, collagen I, collagen III, fibronectin, TGF‑β1, small mothers against decapentaplegic (Smad)2/3, phosphorylated (p)‑Smad2 and p‑Smad3 and were detected using western blot analysis. The data revealed that BA attenuated the CF proliferation and myofibroblast differentiation induced by high glucose. In addition, BA inhibited the expression of extracellular matrix (ECM) in the CFs induced by high glucose. It was also found that BA inhibited the high glucose‑induced phosphorylation of Smad2/3 in the CFs. Taken together, BA suppressed the high glucose‑induced increase in the proliferation of CFs and expression of ECM via inhibition of the TGF‑β1/Smad signaling pathway. Thus, BA may offer therapeutic potential towards the treatment of cardiac fibrosis.