Background　and　aim:　Collagen　fibers　are　the　main　component　of　atherosclerotic　lesions　and　should　therefore　be　used　as　an　index　to　evaluate　plaque　stability.　Although　Masson＇s　trichrome　stainis　usually　employed　to　identify　the　extracellular　matrix,　collagen　fibers　identified　using　this　staining　method　are　difficult　to　analyze　because　the　three　main　colors　often　co-localize　in　same　area　within　the　atherosclerotic　lesion.　To　solve　this　problem,　we　presented　a　convenient　method　for　quantification　of　the　collagen　fibers　in　atherosclerotic　lesions　with　Masson＇s　trichrome　stain.　Methods:　This　method　is　based　on　the　open-resource　image　software　ImageJ　and　an　associated　color　deconvolution　plugin.　Original　images　of　atherosclerotic　lesions　were　converted　into　RGB　images,　and　these　images　were　deconvolved　by　ImageJ　using　the　color　deconvolution　plugin.　Results:　The　resulting　monochromatic　image　obtained　showed　collagen　fibers　in　maximal　separation　from　background　tissues.　To　calculate　the　area　of　the　green　component,　collagen　fibers　were　quantified　in　an　accurate　and　efficient　manner.　Conclusions:　Because　of　the　simplicity　and　accuracy　of　this　method,　it　may　be　widely　applied　for　studying　atherosclerosis　in　humans　or　various　animal　models.