Abstract： Objective:To investigate the clinical and serological characteristics of overlap myositis.Methods:This study was a retrospective study.A total of 108 patients with idiopathic inflammatory myopathies(IIMs)admitted to the department of Rheumatology and Immunology, General Hospital of Northern Theater Command from January 2016 to December 2021 were selected, including 36 males and 72 females, aged(53.59±15.34)years old, ranging from 21 to 83 years old.Patients were divided into overlap myositis group( n=41)and non-overlap myositis group( n=67)according to whether they had overlap myositis or not.The clinical data and laboratory indexes of the two groups were collected. Results:Proportion of women in overlapping myositis group[80.4%(33/41)], mechanic′s hand[17.1%(7/41)], Raynaud′s phenomenon[17.1%(7/41)], interstitial pneumonia[61.0%(25/41)], osteoporosis[21.9%(9/41)]were higher than those in non-overlapping myositis group[58.2%(39/67)、4.5%(3/67)、3.0%(2/67)、35.8%(24/67)、6.0%(4/67)], and the difference was statistically significant( P<0.05). The hemoglobin level in the overlapping myositis group[119.00(109.00, 129.50)g/L]was lower than that in the non-overlapping myositis group[132.50(118.50, 143.00)g/L], and the FT 4 level[13.81(12.11, 16.30)pmol/L]was higher than that in the non-overlapping myositis group[13.81(12.11, 16.30)pmol/L]. The positive rates of antinuclear antibody and anti-RO-52 antibody in the overlapping myositis group[78.0%(32/41)、56.1%(23/41)]were higher than those in the non-overlapping myositis group[35.8%(24/67)、13.4%(9/67)], and the differences were statistically significant( P<0.05). Conclusions:Compared with non-overlapping myositis patients, overlapping myositis patients have lower hemoglobin level, higher FT4 level, higher positive rate of antinuclear antibody and anti-RO-52 antibody, and are prone to be complicated with " mechanic′s hand" , Raynaud′s phenomenon, interstitial pneumonia and other muscle manifestations, and higher incidence of osteoporosis.