Structures of deformed layer generated by cutting of eutectoid steels and effect of cutting conditions were investigated. In cutting of eutectoid steel with spheroidal cementite structure, cementite was hardly deformed but traces caused by deformation of fearlite were observed. The area observed traces increased as rake angle in tool decreased. In cutting of eutectoid steel with pearlite structure, structures of deformed layer were differ in direction to cementite against longitudinal direction to work piece, and in case, direction to cementite was perpendicular to longitudinal direction to work piece, fracture and bend of cementite were observed, and in case, direction to cementite was parallel to it, division, slide and bend were observed. In martensite structure, thick layer was observed to outer layer and size of crystal in this layer was nano level.