Abstract. ECRH experiments have been carried out on HL-1M tokamak (R=102 cm, a=26 cm) since 1999. The electron temperature increases more than 30% of that in ohmic heating. The temperature profile keeps unchanged, but some interesting MHD phenomena, which related with energetic passing or trapped electrons, have been observed. When the plasma current is larger than 150 kA, double sawteeth of soft X-ray appear, indicating that the current density profile or q profile has been changed. Under these conditions the passing fast electrons are dominant. At high ECRH power, when the resonance position is near to the q=1 surface on the high field side, strong m=1 mode appears in the middle of the sawtooth, which would be fishbone-like activities similar to those observed in the PDX tokamak. Addition of lower hybrid waves with middle power to ECRH significantly enhances the MHD excitation, but lower hybrid waves alone cannot excite or sustain the mode. This result is a clear demonstration of the suprathermal trapped electron effect on the instability. The evidence of the existence of the energetic electrons during ECRH can be obtained by hard X-rays.