PURPOSE: To improve the tensile strength and processability of a steel sheet by specifying the content of C, Si, Mn and Al in the steel sheet, subjecting it to hot rolling and thereafter holding its temp. into a specified range to incorporate a specified amt. of retained austenite therein.

CONSTITUTION: A steel slab constituted of, by mass, 0.10 to 0.20% C, ≤0.50% Si, 3.0 to 6.0% Mn and 0.50 to 2.0% Al, and the balance Fe with inevitable impurities is subjected to hot rolling under ordinary conditions. Next, it is held in a ferrite + austenite two-phase region temp. of the Ac1 to the Ac1+50°C for 1 to 20hr and is thereafter subjected to furnace cooling. In this way, the high strength hot rolled steel plate constituted of a composite structure contg. ≥10vol% retained austenite and having a 800N/mm2 class of tensile strength can be obtd.