Objective To study the histological features of plasmacytoid dendritic cells (pDC) in muscle tissue affected by dermatomyositis (DM) and to discuss the pathological significations of pDC.Methods Muscle tissues from 30 cases of DM and 25 cases of polymyositis (PM) were collected.HE stain, immunohistochemistry studies were carried out in all muscle samples.Results Pathological features of DM included: perifascicular atrophy (25/30); punched-out fiber (14/30); perivasculitis (17/30),inflammatory infiltration in the endomysium(6/30).Using immunohistochemistry study, 19 cases from DM were infiltrated by macrophages which are CD68 positive and CD303 negative, 20 cases with DM were infiltrated by pDC which are CD303 positive.The location of pDC were: perivascular of interfascicular septae only (15/20); endomysium only (3/20) and both (2/20).Myopathic damage such as necrotic and regenerating fibers and inflammatory infiltration could be seen in PM.There was few pDC infiltration in PM.Conclusions There is few pDC in muscle tissue affected by PM and many pDC in muscle tissue affected by DM with infiltration mainly in the wide interfascicular septae.pDC may be connected to perifascicular atrophy and play a roll in the pathogenesis of DM.