The antinociceptive effect of epidural administration of huwentoxin I was elucidated in a tonic visceral pain rat model produced by acute colon inflammation. The nociceptive behaviors were induced by perendoscopically injecting dilute formalin (50 μl) into the depth of the colonic wall in rats. Both ω conotoxin MVIIA and morphine hydrochloride were given epidurally as positive control while saline as negative control. Similar to ω conotoxin MVIIA and hydrochloride morphine, the epidural administration of HWTX Ⅰ significantly reduced the nociceptive responses in a dose dependent manner in tonic visceral pain rat model ( P <0 05). The suppression effects of both huwentoxin Ⅰ and ω conotoxin MVIIA at 20 μg/kg were kept steady compared with the saline group and reached their maximum effects at the doses of 50～75 μg/kg within 1 hour when the nociception had been observed. It was also found that at the same doses, huwentoxin Ⅰ was less effective in antinociception than ω conotoxin MVIIA. However, ω conotoxin MVIIA, but not huwentoxin Ⅰ, caused an obvious motor dysfunction at these doses. The action of morphine hydrochloride was initiated faster, but lasted for a shorter time than that of huwentoxin Ⅰ and ω conotoxin MVIIA. Thus, huwentoxin Ⅰ, a potent blocker of neuronal N type voltage sensitive calcium channels, induced a remarkable dose dependent restrain effect similar to ω conotoxin MVIIA and morphine on the tonic visceral pain produced by colonic wall injection of formalin in conscious rats.