Receptor for advanced glycation end products (RAGE) and connective tissue growth factor (CTGF) play a key role in diabetic myocardial fibrosis, and peroxisome proliferator-activated receptor-γ (PPAR-γ) activation has been reported to reduce RAGE and CTGF expression. This study investigated the effects of the PPAR-γ agonist, rosiglitazone, on myocardial expression of RAGE and CTGF, extent of cardiac fibrosis, and left ventricular (LV) diastolic function in type 2 diabetic (T2D) rats. Twenty-week-old T2D rats were randomized to treatment with either 20 weeks of rosiglitazone (20 mg/kg) or saline (n = 10 in each group). Serial echocardiographic examinations were performed just before randomization (20 weeks) and at study completion (40 weeks). Fibrosis extent and RAGE and CTGF expression were assessed in previously imaged hearts by picrosirius red staining, and by real-time reverse transcriptase-coupled polymerase chain reaction (RT-PCR) and immunoblotting, respectively. Results of the latter assessments were further validated by immunohistochemical staining. Rosiglitazone treatment significantly improved E/A ratio in serial echocardiography assessment, and reduced LV collagen volume fraction as demonstrated by picrosirius red staining. Real-time RT-PCR and immunoblots of myocardial tissue from rosiglitazone-treated rats revealed reduced RAGE and CTGF mRNA and protein signals compared to those of saline-treated T2D rats, which were consistent with reduced proportions of myocardial RAGE and CTGF staining in the hearts of T2D rats. PPAR-γ agonist therapy reduces cardiac fibrosis and improves LV diastolic dysfunction as assessed by serial echocardiographic imaging. Suppression of RAGE and CTGF expression in the diabetic myocardium appears to contribute to the antifibrotic effect of rosiglitazone. These results support the potential of PPAR-γ agonists as antifibrotic agents in diabetic cardiomyopathy.