Abstract: Objective To explore the association between arthritis of rheumatic disease and mycoplasma infection by nested-PCR. Methods Mycoplasma, in which ureaplasma urealyticum (Uu) and mycoplasma hominis (Mh) and mycoplasma fermentans (Mf) and mycoplasma arthritis (Mar) were studied in the synovial fluid of patients suffering from different arthritis by nested-PCR. There were about fifty-nine patients, twenty-six patients with rheumatoid arthritis (RA), twenty-four patients with reactive arthritis (ReA), three patient with systemic lupus eryrhmatosus(SLE),one patients with sjogran's syndrom(SS),one patient with osteoartheitis(OA),one patient with undifferentiation tissue (UCTD),three patients with ankylosing spondylitis(AS).Results Uu was detected in 2 of 26 RA and 2 of 24 ReA and 1 of 3 SLE patients,Mh was detected in 1 of 26RA and 1 of 24 ReA and 2 of 3 SLE and 2 of 24 ReA and 1 of 3 SLE patients,Mh was detected in 1 of 26 RA and 1 of 24 ReA and 2 of 3 SLE and 1 SS patients.Mar was detected in 1 of 26 RA patients.Conclusions There was association between arthritis of rheumatoid disease and mycoplasma infection.Mycoplasma may be important agent in the etiology of rheumatoid disease.