ObjectiveTo explore the value of differential diagnosis between pigmented villonodular synovitis (PVNS) and rheumatoid arthritis (RA) in active stage with clinic and ultrasound. MethodsWe analyzed retrospectively the characters of clinic and ultrasound of sixteen patients with PVNS and sixteen patients with rheumatoid arthritis inactive stage.ResultsIn aspects of patient’s age (T=185), pain scores (T=136) history of trauma (P=0.029), functionally uncompensated conditions (P=0.001) type (P=0.000) and sum (P=0.000) of involved joints、bright spot-echoes in hydrops (P=0.001) tendons nearby involved (P=0.001) and the Adler’s grade of Doppler ultrasound blood flow (P=0.009), the differences between PVNS and RA in active stage had statistical significance (P<0.05). Clinic characters: patients with PVNS were younger, often had a history of trauma. But patients with RA in active stage had a higher pain score and functionally uncompensated condition. Ultrasound characters: big and single joints were often involved in patients with PVNS, and tiny bright spot echoes could be detected in hydrops. Instead, big and small, multiple joints, tendons nearby were often involved in patients with RA, who had a higher ratio of gradeⅢ Doppler ultrasound blood flow. And in aspects of sex, the presence of hydrops and synovium thickness, the differences between the two had no statistical significance (P>0.05).ConclusionThe clinical characters including Patient’s age, pain scores, history of trauma, functionally uncompensated conditions, and the characters of ultrasound including type and sum of involved joints, bright spot echoes in hydrops, tendons nearby involved and the Adler’s grade of Doppler ultrasound blood flow, are helpful for the differential diagnosis of PVNS and RA in active stage.