Objective To investigate the vasorelaxant effect and possible mechanism of niclosamide ethanolamine (NEN) on isolated rat coronary artery (RCA). Methods Wire myograph was used to record myogenic tone of vessels. The vasorelaxant effect of NEN was studied in RCA precontracted with either KCl or U46619. Study of related inhibitors was performed to investigate possible involvement of potassium channels and the mitogen-activated protein kinase (MAPK) signaling pathway in vasorelaxation. The effect of NEN on Ca^{2 +} mobilization was determined by observing vasoconstrictor-induced contractions in tissue solution deprived of Ca^{2 +} followed by Ca^{2 +} restoration. Results NEN (0.5 -3.0 μmol/ L) relaxed RCA precontracted with KCl or U46619 in a concentration-dependent manner. MAPK inhibitors (PD98059 and SB239063) reduced the relaxant effect of NEN, while the potassium-channel blockers (tetraethylamine, 4-aminopyridine, BaCl2 , and glibenclamide) did not significantly affect relaxation. NEN specifically inhibited the contraction component dependent on extracellular Ca^{2 +} influx in vessels stimulated with KCl and U46619, with a negligible effect on the component dependent on intracellular Ca^{2 +} release. Conclusions NEN exhibits vasodilator properties in RCA. Inhibition of extracellular Ca^{2 +} influx and activation of the MAPK signaling pathway may be involved in NEN-induced RCA vasorelaxation.