Objective: The modulatory effects of nociceptin/orphanin FQ ( OFQ) on acupuncture ( EA, a odern version of acupuncture)-induced analgesia are still controversial. Transgenic OFQ knock-out mice rovide us a useful tool to investigate the role of endogenous OFQ in EA analgesia. The present tudy aims to investigate the role of OFQ in the EA-induced analgesia with OFQ knock-out mice. ethods; Acupoints were selected as "Zusanli" (ST36) and "Sanyinjiao" (SP6) , EA parameters were as ollows; constant current output, rectangular (square) wave pulses, increased intensities of 0. 5, 0. 7,0. 9 mA with stepwise fashion, 10 min for each intensity, frequency of 100 Hz (with 0. 2 ms as ulse width) or 2 Hz ( with 0. 6 ms as pulse width). Tail flick latency (TFL) evoked by radiant heat was used to evaluate the change of pain threshold before, during and after EA application. Thenock-out mice were divided randomly into 3 groups; needling control, EA at 100 Hz and 2 Hz. ild-type mice of litter-mates of were used as Control. Results: It was found that OFQ knock-out mice had a longer basal ther-mal threshold; EA had enhanced analgesic effect in the knock-out mice than in wild-type Control mice. Conclusion: Endogenous OFQ might be algesic in basal condition and antagonize EA analgesia.