Deformation induced martensite transformation in hot-rolled multiphase steels containing retained austenite was studied to elucidate the relationship between the stability of retained austenite and the flow behavior depending on compositions and process conditions. The change in volume fraction of retained austenite with strain was studied on two basically different kinds of kinetics model, treated as a function of strain in one model and stress in the other model. It is shown in the present study that the latter model (stress) has the clearer physical meaning. A new Rinetics equation for deformation induced transformation was formulated as log f_γ=log f_(γ0)-δ(σ-σ_(YS)), with parameter δ characterizing the stability of retained austenite. The increase in plastic stability of retained austenite with the increase in carbon content in retained austenite can be explained by the increase in the mechanical driving force for martensite transformation.