Decomposition kinetics of undercooled austenite of the medium carbon Cr-Ni-Mo steels within the pearlite region is studied by the dilatometric and metallographic methods. An existence of small-amplitude oscillations of the decomposition rate is ascertained. The experimental curve of 'decomposition rate of undercooled austenite-time of isothermal holding' is obtained for 38Kh2NM steel. It is shown that the decomposition process includes two independent processes in the local regions with the own kinetics depending on polymodal grain structure of austenite primarily.