The torsion tests of 304 stainless steel were performed in the temperature range of 900~1100℃ and strain rate range of 5.0×10(-2)~5.0×10(0)/sec to study the high temperature softening behavior. The flow curves and microstructures showed the behavior of dynamic recrystallization (DRX). The dependence of temperature(T) and the stain rate(ε) on the flow stress was expressed by the hyperbolic sine law, ε=2.75×10(14) (sinh 0.076δ)(5.26) exp(-379000 J/mol/RT). The dynamically recrystallized gram size(d(DRX)) was related to the value of the Zener-Hollomon parameter Z. Under the Z value of 10(17), it was found that the grain size ranged from 10 to 20㎛. The relationship between the dynamically recrystallized grain size and Z paramet­er was found as follows: d(DRX)=139.48-7.33 log Z and the calculated grain sizes were well matched with the experimental values. To determine the optimum condition of plastic deformation, the deformation map was made from the efficiency of power dissipation. The maximum efficiency was 0.41 at the condition of 1100℃, 0.5/sec, 100%.