In order to observe antinociceptive effect of Oxymatrine (OMT) and its effect on voltage-activated K(+) channel, the acetic acid-induced abdominal contraction model of mouse was used to test the antinociceptive effect in vivo, and in vitro, the delayed rectifier K(+) currents (Ik) in PC12 cells (rat pheochromocytoma cells) was recorded using the automated patch-clamp method. The results indicated that after application of OMT, the number of acetic acid-induced animal abdominal contraction was significantly decreased, Ik in PC12 cells was significantly decreased, and showed a concentration-dependent manner. After application of OMT, both the activation and inactivation curves of Ik of PC12 cells were shifted to negative potentials. This study revealed that OMT showed antinociceptive effect in mice. The inhibition of voltage-activated K(+) channel might be one of mechanisms in which the enhanced both activation and inactivation of K(+) channel were involved and might play important roles.