The torsion tests in the range of 790∼1100℃, 3.7×10^(-1)∼5.0×10^0/sec were performed to study the high temperature continuous deformation behavior of Nb-microalloyed structural steels and carbon steel. The flow curves exhibited the characteristic of dynamic recrystallization(DRX). The dependence of the flow stress on temperature(T) and stain rate(ε·) was expressed by power law, ε˙ = A(σ^n′)_pexp(-Q/RT). The dynamically recrystallized grain related to the value of the Zener-Hollomon parameter Z. Under the Z value of 10^(13) order it was found that the grain size ranged from 20㎛ in Nb microalloyed steel to 30㎛ in carbon steel.