Objective:To compare the effect of 2 Hz or 100 Hz transcutenous electrical nerve stimulation(TENS) on treating chronic pain with adjuvant monoarthritis in rats,and discuss changes of opioid peptide and anti-opioide peptide related to therapy effect.Methods:Water-in-oil type complete Freund’s adjuvant(CFA) was injected into the right tibio-tarsal joint to produce a monoarthritic model. After treated with TENS,the content of CCK-8,OFQ and EM2 was measured by radio-immunoassay in spinal perfusate and dorsalhalf of the spinal cord. Results:①2~5 weeks after arthritis,the content of CCK-8 in spinal cord was increased significantly(P < 0.05,P < 0.01),100 Hz TENS postponed peak time of CCK-8 from 2nd week to 3rd week.②100 Hz TENS was more effective than 2 Hz TENS in increasing content of OFQ. ③1~9 weeks after arthritis,the content of EM2 in spinal cord was decreased significantly(P < 0.01),100 Hz TENS postponed peak time of EM2 to 2nd week,and both 2 Hz and 100 Hz TENS can lead content of EM2 to normal during later period of arthritis(5~9 weeks). Conclusion:Changes of neuropeptide in spinal cord related to analgesia could take place in different degrees during arthritis,and different influence on opioide and antiopioid peptide might be involved in the mechanism of variation between two therapeutic effects of 2 Hz and 100 Hz TENS.