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AIM This study was designed to assess the antinociceptive effect of verticinone and to evaluate the involvement of opioid receptors activation.METHODS In vivo nociceptive response was induced by hot-plate test and the hind paw withdrawal latencies (HWLS) of mice during thermal stimulation were measured before and repeated at 10, 15, 30, 45 and 60 min after verticinone(0.5 mg·kg-1, icy.) administration.In vitro guinea pig ileum(GPI) bioassay is relatively selective for mu opioid receptor and is used for define the action of mu drugs.The inhibitory effect of verticinone on electric stimulus-induced contration of myenterio plexuslongitudinal muscle strip (MPLM) from GPI was observed.RESULTS Verticinone(0.5 mg·kg-1, icv.) presented anticociceptive effect in hot-plate test in mice and the effect was completely prevented by naloxone, the non-selective antagonist at mu, delta, and kappa opioid receptor.In vitro study in the MPLM from GPI verticinoe showed weak inhibition on the electric stimulus-induced contraction, and the effect could not be reversed by naloxone, while morphine inhibited electric stimulus-induced contraction of MPLE from GPI and the effect can be reversed by naloxone.CONCLUSION The antinociceptive effect of verticinone probably is related to its activation of delta or kappa opioid receptor, but not mu-opioid receptor.