The deformation microstructure produced by heavy cold rolling (from 70% to 95% reduction) of pearlitic structure with various amounts of rolling and the tensile strength of the cold rolled sheets were studied in the plain carbon steels with various carbon contents (0.6, 0.76, and 1.0 mass%C). The deformation microstructure was classified into the following three types; 1) Irregularly Bent Lamella (IBL): lamellae originally inclined with large angles to the rolling plane and irregularly bent after deformation, 2) Coarse Lamella with Shear band (CLS): the rhomboidal blocks of weakly deformed lamellae bounded by shear band, 3) Fine Lamella (FL): heavily deformed lamellae aligned parallel to the rolling direction with fine interlamellar spacings. As rolling reduction increases, the proportion of FL increases. The tensile strength of cold rolled specimens increases with rolling reduction. Work hardening with respect to true strain by cold rolling is similar to that obtained by wire drawing. After 92% cold roiling of 1.0 mass%C steel, the tensile strength over 2 500 MPa was achieved.