Breast　cancer　can　be　cured　by　early　diagnosis.　Appropriate　and　effective　clinical　treatment　benefits　from　accurate　pathological　diagnosis.　However,　due　to　the　lack　of　effective　screening　and　diagnostic　imaging　methods,　early　stages　of　breast　cancer　often　progress　to　malignant　breast　cancer.　In　this　study,　multiphoton　microscopy　(MPM)　via　two-photon　excited　fluorescence　combined　with　second-harmonic　generation　was　used　for　identifying　the　early　stages　of　breast　ductal　carcinoma.　The　results　showed　differences　in　both　cytological　features　and　collagen　distribution　among　normal　breast　tissue,　atypical　ductal　hyperplasia,　low-grade　ductal　carcinoma　in　situ,　and　high-grade　ductal　carcinoma　in　situ　with　microinvasion.　Furthermore,　three　features　extracted　from　the　MPM　images　were　used　to　describe　differences　in　cytological　features,　collagen　density,　and　basement　membrane　circumference　in　the　early　stages　of　breast　ductal　carcinoma.　They　revealed　that　MPM　has　the　ability　to　identify　early　stages　of　breast　ductal　carcinoma　label-free,　which　would　contribute　to　the　early　diagnosis　and　treatment　of　breast　cancer.　This　study　may　provide　the　groundwork　for　the　further　application　of　MPM　in　the　clinic.　©　2020　Zhong　Chen　et　al.