The effect of deformation on martensitic transformation in austenitic stainless steel type 304 was studied by using the magnetic method on samples subjected to subsequent quench in liquid nitrogen after tensile deformation at 200°C. The results show that formation of quench-induced α′ martensite is very sensitive to plastic strain, and unlike that induced by deformation, its amount decreases with increasing strain. Furthermore, the coercivity of quench-induced α′ martensite also exhibits a trend opposite to that of deformation-induced martensite.