Abstract: The structural phase transition of the bainitic spheroidal graphite cast iron is studied by Mössbauer spectroscopy. We find that the structural phase transition occurs after the applied s rain, that the more the strain, the more the transition of ehe retained austenite, and that the amount of decrease of the retained austenite is tqual to the amount of increase of bainite, which is about 6% for the strain of 9.8%. It seems that there exist two bainitic structures for the bainitic spheroidal graphite cast iron.