To provide a better understanding of the mechanical properties of high Cr-low Ni two-phase stainless steels, tensile behaviors at low temperature as well as at room temperature and the effect of strain aging on them were studied. Materials used in this report were three kinds of (α+γ) two-phase stainless steels containing 25% Cr and, 4, 7 and 10% Ni. Specimens which were annealed mainly at 900°C were studied and the principal results were as follows. (1) Shape of the stress-strain diagrams at room temperature is identical to that of common materials without yield point. However, at −196°C a phenomenon similar to the so-called yield point can be observed after a few percent deformation in the 4 and 7% Ni specimens, containing 40 and 50% γ phase, respectively. (2) This phenomenon can also be observed in both specimens annealed at 1000°C, but disappears as the annealing temperature rises to 1100°C. It becomes obscure as the testing temperature decreases to −78°C. (3) Strain hardening rate during the uniform plastic deformation of the specimens with 4 and 7%Ni, especially 4% Ni, at −196°C is very large for a wide range of strain and this is also found to occur at −78°C. However, uniform elongations at −196°C are as large as those at room temperature in all cases. (4) In the specimens with 7% Ni, as the amount of predeformation by tension at −196°C increases the tensile strength at room temperature increases greatly. (5) Strain aging appears in every specimen and its extent becomes more prominent as the Ni content decreases and the a phase increases. (6) The above-mentioned yield point phenomenon, the increase in strain hardening rate and the increase in tensile strength by predeformation are all due to the formation of the deformation-induced martensite from the γ phase. On the other hand, the a phase plays an important role in the strain aging.