Abstract: Dilatometric studies on X12CrMoWVNbN1011 ferrite heatresistant steel were carried out to investigate the martensitic transformation under different austenization conditions. When the austenitizing temperature increases from 1 010 ℃ to 1 200 ℃ and the holding time keeps at 15 min, Ms and Mf increase with the increasing of austenitizing temperature. When the austenitizing temperature keeps at 1 070 ℃ and the holding time changes from 5 min to 20 h, Mf increases with the increasing of the holding time, and Ms increases with the increasing holding time only for the first 3 h, and then reaches a constant value of 460　℃　when the holding time exceeds 3 h. A new kinetic equation for martensitic transformation for this steel austenitized at 1 070 ℃ was obtained based on the dilatometric curves tested, which sets up the relationship between the volume fraction of martensite, transformation temperature and the austenization holding time.