This study was conducted to examine telomere biology in terms of improving insulin sensitivity in a type 2 diabetic animal model, OLETF (OL) rats. To improve insulin sensitivity, pioglitazone (10 mg /Kg/day) was administrated to OL rats from 20 weeks to 40 weeks of age, and the effects of treatment were compared to that in untreated OL or control LETO rats. At the end of the study, HOMA-IR significantly increased in OL rats, but decreased in OL rats treated with Pioglitazone (OLP). No shortening of telomere length was observed in the heart tissues of OL rats, whereas telomerase activity was decreased in OL heart tissue. The mRNA expression of both telomerase reverse transcriptase and telomere repeat binding factor 2 was downregulated in the hearts of OL rats. Protein expression of phospho-Akt, insulin-like growth factor, and endothelial nitric oxide synthase was reduced in OL rats. On the other hand, myocardial MMP-9 expression was elevated in OL rats. The changes observed in OL rats were inhibited by pioglitazone treatment. However, the protein and mRNA expression of Sirt1, a life-span modulator, was attenuated in the OL rat heart, although it was enhanced in OLP rats. Myocardial fibrosis was less extensive, and diastolic dysfunction more greatly ameliorated, in OLP than in OL rats. These findings suggest that improving insulin sensitivity via the activation of PPAR- may exert regulatory effects on cardiac telomere biology and may have desirable morphological and functional effects on the diabetic heart.