We prepared methotrexate (MTX)-encapsulated nanoparticles of water-soluble chitosan. MTX-encapsulated nanoparticles of WSC was prepared by mixing of MTX/DMSO solution into chitosan/deionized water. MTX-encapsulated nanoparticles of Chitosan has spherical shapes and particle size was around 200nm at TEM observation. In 1H-NMR study, the specific peaks of MTX and Chitosan was observed at nanoparticles in DMSO while specific peaks of MTX was disappeared at D2O, indicationg that MTX was encapsulated into inner-part of nanoparticles. Resultantly, MTX was incorporated into WSC via ion complex formation between MTX and chitosan mainchain. Thus, MTX-incorporated nanoparticles of WSC are expected to potential carrier for autitumor targeting.