A 2-Benzyl-5-hydroxy-6-methoxy-3, 4-dihydroisoquinolin-1-one (ZC2) is a newly synthesized isoquinolinone compound. Its effect on vasodilation was evaluated in the present study. Isometric tension of rat artery rings was recorded by a sensitive myography system in vitro. The results showed that ZC2 relaxed rat mesenteric arteries pre-contracted by KCl, phenylephrine and 9, 11-dideoxy-$11{alpha}$, $9{alpha}$-epoxymethano-prostaglandin $F2{alpha}$ (U46619), and abdominal aorta pre-contracted by KCl in a concentration-dependent manner. The ZC2-induced vasodilation was not affected by an endothelium denudation. ZC2 rightwards shifted the concentration-contraction curves, induced by KCl, phenylephrine, and 5-hydroxytryptamine (5-HT) in a non-parallel manner, which suggests that the vasodilation effects are most likely via voltage-dependent calcium channel (VDCC) and receptor-operated calcium channel (ROCC). Moreover, in $Ca^{2+}$-free medium, ZC2 concentration-dependently depressed the vasoconstrictions induced by phenylephrine and $CaCl_2$, and decreased a contractile response induced by caffeine, which indicates a role of extracellular $Ca^{2+}$ influx inhibition through VDCC and ROCC, and intracellular $Ca^{2+}$ release from $Ca^{2+}$ store via the ryanodine receptors. Glibenclamide did not affect the vasodilation induced by ZC2, suggesting that ATP sensitive potassium channel is not involved in the vasodilation. The results indicate that ZC2 induces vasodilation by inhibiting the VDCC and ROCC, and receptor-mediated $Ca^{2+}$ influx and release. The inhibition of intracellular $Ca^{2+}$ release may be mediated via the ryanodine receptors.