Aims of study. The aim of the present study was to investigate whether an ethanol extract of Scutellaria baicalensis (ESB) relaxes penile corpus cavernosum muscle in organ bath experiments. Materials and methods. Changes in tension of cavernous smooth muscle strips were determined by penile strip chamber model and in penile perfusion model. Isolated endothelium-intact rabbit corpus cavernosum was precontracted with phenylephrine (PE) and then treated with ESB. Results. ESB relaxed penile smooth muscle in a dose-dependent manner, and this was inhibited by pre-treatment with N(G)-nitro-l-arginine methyl ester (l-NAME), a nitric oxide (NO) synthase inhibitor, and 1H-[1, 2, 4]-oxadiazolo-[4,3-α]-quinoxalin-1-one (ODQ), a soluble guanylyl cyclase (sGC) inhibitor. ESB-induced relaxation was significantly attenuated by pretreatment with tetraethylammonium (TEA), a nonselective K(+) channel blocker, and charybdotoxin, a selective Ca(2+)-dependent K(+) channel inhibitor. ESB increased the cGMP levels of rabbit corpus cavernosum in a concentration-dependent manner without changes in cAMP levels. In a perfusion model of penile tissue, ESB also relaxed penile corpus cavernosum smooth muscle in a dose-dependent manner. Conclusion. Taken together, these results suggest that ESB relaxed rabbit cavernous smooth muscle via the NO/cGMP system and Ca(2+)-sensitive K(+) channels in the corpus cavernosum.