Polygonum cuspidatum (PC) has been used for the treatment of arthritis and urinary diseases in traditional medicine. Despite recent evidence that PC has anti-oxidant, anti-tumoral, and anti-inflammatory effects, analgesic and anti-inflammatory effects of PC have not been elucidated yet in vivo. Thus, in the present study, analgesic and anti-inflammatory effects of ethyl acetate extract of PC (EAPC) were investigated in vivo for the first time. Hot plate test and tail-flick test revealed that EAPC at 200 mg/kg exerts analgesic effect (p < 0.05). In contrast, EAPC did not show significant analgesic effect in acetic acid-induced writhing test. Serotonin-induced paw edema model and Freund's complete adjuvant (FCA)-induced adjuvant arthritis model were used to examine anti-inflammatory effect of EAPC in vivo. In serotonin-induced paw edema model, EAPC suppressed swelling inflammatory response within 12 min after serotonin injection, at both 100- and 200-mg/kg dose (p < 0.05). Consistently, in FCA-induced adjuvant arthritis model, FCA at 200 mg/kg significantly suppressed FCA-induced joint swelling within 3 days (p < 0.05), whereas FCA at 100 mg/kg showed the similar result within 5 days (p < 0.05). Furthermore, EAPC effectively inhibited positive responses of c-reactive protein and rheumatoid factor compared to untreated control. Taken together, our findings suggest that EAPC can be a potent candidate for rheumatoid arthritis treatment.