PURPOSE: To manufacture the steel sheet as rolled excellent in the toughness of the base body itself and toughness along its thickness, by uniformly strain-hardening austenitic grains before being transformed in very low or low-carbon steel having specified compositon, so as to obtain the tough structure composed of uniform fine grains after being transformed.

CONSTITUTION: Steel contg., by wt%, 0.01W0.2% C, Si≤1.5%, 0.5W3% Mn, and one or more of Nb≤0.1%, V ≤0.1%, Ti≤0.3% and Zr≤0.3% is hot-rolled as follows. It is rolled with accumulated reduction ratio of 10W60% in the temp. zone where austenite is partially recrystallized during a rolling pass, to introduce prestrain into the specified austenitic grains. Thereafter, it is rolled with accumulated reduction ratio above 40% in the temp. zone where austenite is not recrystallized yet, to uniformly strain-harden the whole of austenitic grains. In addition, the ratio of accumulated redution below Ar3 transformation point (the dual phase zone) is made below 30% when the rolling is finished.