Abstract. Plasma perturbations and sequence of events leading to a sawtooth instability are studied in T-10 tokamak (R=1.5 m, a=0.3 m) in ohmically and ECRH heated plasma. Analysis of the experiments indicated generation of the non-thermal x-ray spikes (E25-100 keV) around X-points of the m=1, n=1 magnetic island. The spikes could be connected with generation of the non-thermal electrons during magnetic reconnection. Results of the experimental studies of the plasma perturbations during sawtooth crash are compared with modelling of generation of the non-thermal electron beams in strong electric fields. Analysis indicted that the suprathermal beams induced during the reconnection can change magnetic shear around the q=1 surface and modify dynamic of the sawtooth crash.