This study was carried out to investigate the effects of GCP treatment on the expression of NOS, c-fos, serotonin and substance P in central nerve system of monosodium iodoacetate(MIA)-induced osteoarthritic pain model. Arthritis was induced by injection of MIA(0.5 mg) into knee joint cavities of rats. Arthritic rats were divided into control(n=8) and treated(n=8) group. Control group was taken distilled water for 20 days. Treated group was taken extracts of GCP by oraly for same duration. Normal group(n=8) was infected with normal saline and was taken distilled water for 20 days. The numbers of NADPH-d positive cells in superficial dorsal horn of spinal cord of treated group($21{pm}5$) was significantly (p<0.01) decreased compared with control($33{pm}5$). The numbers of NADPH-d positive cell in dorsolateral periaqueductal gray matter of treated group($111{pm}16$) was significantly(p<0.01) decreased compared with control($143{pm}14$). The numbers of c-fos positive cells in dorsal periaqueductal gray matter of treated group($57{pm}16$) was significantly(p<0.01) decreased compared with control($78{pm}13$). The numbers of c-fos positive cells in paraventricular thalamic nucleus of treated group($60{pm}15$) was significantly decreased compared with control($88{pm}27$). The numbers of serotonin positive cells in median raphe nucleus of treated group($171{pm}31$) was significantly(p<0.05) decreased compared with control($217{pm}48$). On the basis of these results, we concluded that GCP treatment has inhibiting effects on the pain transmission in monosodium iodoacetate-induced osteoarthritic pain model in rat.