Spectral analysis was made for mesospheric radial wind velocities estimated from the measurement of Doppler-shifted echo power by the MU radar at Shigaraki (34.9¿N, 136.1¿E), Japan. In this paper we give an overview of the data and present the frequency spectra of the radial winds at altitudes of 74 to 77 km. Under quiet wind conditions, the frequency spectra for the vertical winds show an almost flat response in between the inertial and Brunt-V¿is¿l¿ (fB) frequencies with the peak at a frequency a little lower than fB. The frequency spectra for the other oblique winds have an approximate f-2 spectral slope with a weak peak at the same frequency as the vertical one. These features are consistent with the results given by a theoretical spectral model of gravity waves and suggest that the observed wind fluctuations are caused by gravity waves. ¿ American Geophysical Union 1990