Glucocorticoids are the primary hormones that respond to stress and protect organisms from dangerous situations. The glucocorticoids hydrocortisone and its dormant form, cortisone, affect the cardiovascular system with changes such as increased blood pressure and cardioprotection. Kv1.5 channels play a critical role in the maintenance of cellular membrane potential and are widely expressed in pancreatic β-cells, neurons, myocytes, and smooth muscle cells of the pulmonary vasculature. We examined the electrophysiological effects of both cortisone and hydrocortisone on human Kv1.5 channels expressed in Xenopus oocytes using a two-microelectrode voltage clamp technique. Both cortisone and hydrocortisone rapidly and irreversibly suppressed the amplitude of Kv1.5 channel current with IC50 values of 50.2±4.2 μM and 33.4±3.2 μM, respectively, while sustained the current trace shape of Kv1.5 current. The inhibitory effect of cortisone on Kv1.5 decreased progressively from −10 mV to +30 mV, while hydrocortisone's inhibition of the channel did not change across the same voltage range. Both cortisone and hydrocortisone blocked Kv1.5 channel currents in a non-use-dependent manner and neither altered the channel's steady-state activation or inactivation curves. These results show that cortisone and hydrocortisone inhibited Kv1.5 channel currents differently, and that Kv1.5 channels were more sensitive to hydrocortisone than to cortisone.