The stabilization of retained austenite was studied via a two-step cooling procedure. Alloys with M(s) temperatures below 0 degrees C were used. It was found that the martensitic transformation starting temperature, M(s), was lowered to M(s)' during the second step of cooling. With increasing the amount of previously formed martensite, the difference in the transformation starting temperatures, Delta M(s) (= M(s) - M(s)'), increases. This stabilization effect can also be observed in an alloy having very low carbon content, and the magnetic properties of alloys do not have drastic effect on the nature of this stabilization phenomenon. The mechanism of the stabilization of retained austenite is proposed to be mainly due to the inhibition effect produced by the previously formed martensite. The aging processes are considered to be a necessary condition for the above mechanism to operate.