Previous studies have shown that exercise training influences potassium channel protein expression in arteries. The purpose of this study was to investigate the effect of exercise training on alterations in voltage-gated potassium channels (K_v) and large-conductance, calcium-activated potassium channels (BK_Ca) in thoracic aorta smooth muscle cells from spontaneously hypertensive rats (SHRs). Male SHRs were randomly assigned to a sedentary group (SHRSED) and exercise training group (SHR-EX). Age-matched Wistar-Kyoto rats (WKYs) were used as controls. After 8 weeks of aerobic exercise training, blood pressure was significantly lower in the SHR-EX group than in the SHR-SED group. Exercise training increased the contribution of the K_v 1.2 and K_v 1.5 channels and decreased the contribution of BK_Ca channel to resting tone in the SHR-EX group compared to the SHR-SED group as indicated by vessel contractility experiments. Immunohistochemistry and Western blotting showed that K_v 1.2 and K_v 1.5 channel expression was significantly lower in the SHR-SED group than in the WKY group and exercise training attenuated this reduction. BK_Ca α-subunit expression was statistically unchanged between the groups; however, β1-subunit expression was reduced significantly by exercise training in the SHR-EX group compared to the SHR-SED group. These data suggest that exercise training reverses the pathological expression of the K_v 1.2, K_v 1.5, and BK_Ca channels in aortic myocytes from SHRs. This is one of the favorable effects of exercise training on large conduit arteries.