Pioglitazone has been shown to reduce the occurrence of fatal and nonfatal myocardial infarction (MI) in type 2 diabetes mellitus (DM). However, the mechanisms of such favorable effects remain speculative. The aim of this study was to investigate the effect of pioglitazone on arterial baroreflex sensitivity (BRS) and muscle sympathetic nerve activity (MSNA) in 30 DM patients with recent MI. Patients were randomly assigned to those taking pioglitazone (n = 15) and those not taking pioglitazone (n = 15) at 4 weeks after the onset of MI. BRS, MSNA, calculated homeostasis model assessment of insulin resistance index (HOMA-IR), and plasma adiponectin were measured at baseline and after 12 weeks. Pioglitazone increased plasma adiponectin (from 6.9 ± 3.3 μg/dL to 12.2 ± 7.1 μg/dL) and reduced HOMA-IR (from 4.0 ± 2.2 to 2.1 ± 0.9). In the pioglitazone group, MSNA decreased significantly (from 37 ± 7 bursts/min to 25 ± 8 bursts/min) and BRS increased significantly (from 6.7 ± 3.0 to 9.9 ± 3.2 ms/mm Hg) after 12 weeks. Furthermore, a significant relationship was found between the change in MSNA and HOMA-IR (r = 0.6, P = 0.042). Thus, pioglitazone decreased the sympathetic nerve traffic through the improvement of insulin resistance in DM patients with recent MI, which indicate that the sympathoinhibitory effects of pioglitazone may, at least in part, have contributed to the beneficial effects of pioglitazone.