Continuous observations over three weeks were performed with the MU radar at Shigaraki, Japan (35N, 136E) in April of 1995. By integrating radar echo spectra over 30 min after removing severe interferences, winds were successfully estimated offline up to 24 km in the lower stratosphere. It was found that inertia-gravity waves with a period of about 20 h and a vertical wavelength of 3.5 km are dominant near 22 km in a region of weak background winds. Four wave packets were fitted to plane waves by a least-squares method and wave parameters were estimated theoretically. The inertia-gravity waves propagate energy upward, and their horizontal phase velocity is westward in the range -10 to -20 m s-1. The waves have large momentum fluxes of about -0.002 Nm-2. This result suggests that inertia-gravity wave drag may contribute to the formation of easterlies in the summer stratosphere.¿ 1997 American Geophysical Union