Quasi-monochromatic waves with an electrostatic nature in the lower hybrid frequency range have been identified in the plasma sheet boundary layer at XGSM=-49Re and -69Re by the wave-form observations in a band 0--25 Hz from the double probe onboard the GEOTAIL spacecraft. Simultaneous measurements of low energy ions also indicate that the wave coincides with the transition of the ion-energy from 0.1 to keV/e to 10 keV/e. ¿ American Geophysical Union 1994