Abstract: Objective To study the antinociceptive effect of intrathecally administered huwentoxin-I (HWTX-I or HWAP-I) on visceral pain in rats with acute colon inflammation. Methods Nociceptive behaviors was induced by formalin injected into the submucosa of the sigmoid colon in rats and the typical behavioral patterns induced served as the indexes for visceral nociception scoring. HWAP-I (0.1-1.0 μg/kg·b.w.), SNX-111 (0.2, 0.5 and 0.75 μg/kg·b.w.) and morphine hydrochloride (0.05, 0.1 and 0.2 μg/kg·b.w.) were administered subarachnoidally 30 min before formalin injection. Results Similar to SNX-111 and hydrochloride morphine, HWAP-I administered subarachnoidally significantly reduced nociceptive responses in a dose-dependent manner in the rat model of visceral pain (P<0.05). Both HWAP-I and SNX-111produced pain suppression effect at the dosage of 0.2 μg/kg·b.w., and in spite of the stronger antinociceptive effect of SNX-111 than HWAP-I at the same doses, SNX-111 caused obvious motor dysfunction in the rats at the doses higher than 0.5 μg/kg·b.w., which was not observed with HWAP-1 at such doses. The antinociceptive effect of morphine hydrochloride was initiated faster but lasted for a shorter period of time than the effects of HWAP-I and SNX-111. Conclusion As a potent blocker of neuronal N-type voltage-sensitive calcium channel, HWAP-I induces remarkably dose-dependent inhibitory effect similar to SNX-111 and morphine on visceral pain induced by sigmoid colon submucosal injection of formalin in conscious rats.