ObjectiveTo search the serum proteins with differentially expression in patients with polymyositis (PM) with or no with Interstitial Lung Disease (ILD).Methods3 PM patients, 3 PM+ILD patients and 3 healthy controls were included in our study.The proteins in serum were separated by two-dimensional electrophoresis.The proteins with significant differential expression (ratio>2 and anova≤0.05) among three groups were identified by matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry (MALDI-TOF-MS)．The results were certified by ELISA.ResultsWe identified 9 proteinsfrom 15 differential protein points by MS.Compared with healthy controls, 4 differential proteins espressed significantly highly that amyloid A protein,apolipoprotein A1, Serum albumin, and Clusterin, but Serotransferin （TRF）significantly declined in the PM patients.Compared with healthy controls, the expression of 4 differential proteins that serotransferrin, zinc-a2-glycoprotein, a2-H2-glycoprotein, a1-beta glycoprotein significantly declined in the PM+ILD patients.Compared with PM group, the expression of β2-glycoprotein 1 and serotransferrin significantly decreased in the PM+ILD patients.We found that the expression of TRF has no difference in all groud by ELISA.ConclusionThere were 8 kinds differential espressed protein among PM, PM+ILD and healthy controls, and these proteins were likely to be the pathogenetic protein of polymyositis involve in progress of the disease.