The microstructure and tensile properties of low carbon 2% Mn steel and 2% Mn-Nb-V steel that had been cold rolled by different degrees of reduction, were studied after aging treatment at 500, 600 and 700℃ for 60 minutes The specimens of 50% cold reduction show higher strength than those of 25% cold reduction, when aged at 500 and 600℃. However, this trend is reversed when they are heat treated at 700℃, in the temperature range of α＋γ region of those steels. Effects of aging treatments at 600℃ are also investigated for the periods of times up to 3,000 minutes. By increasing the aging time the ferrite grains recrystallize progressively and become equiaxed, and the carbides coarsen. Carbides in Mn-Nb-V steel are analyzed as V₄C₃and NbC by the election diffraction method.