The J=61,5-60,6 (110.836 GHz) line of stratomesospheric O3 has been measured employing a Nb SIS mixer receiver cooled by a closed cycle 4 K refrigerator on the Higashiyama Campus of the Nagoya University (35 ¿N, 137 ¿E, 70 m above sea level) since January 1992 in a sporadic manner. Relative diurnal variations of O3 in January 1995 are in good agreement with a zero-dimensional model, ignoring transport in the 3.2 to 0.1-hPa range. Time profiles of the O3 mixing ratio in dawn and dusk are shown with a time resolution of 6 min in the step of 0.25 of log10p, where p denotes the total atmospheric pressure in hectopascals. Amplitudes of seasonal variations are small at around 20, 3.2, and 0.056 hPa, respectively, and the type or phase of seasonal variations changes at these altitudes. Mixing ratio is high in summer between 10 and 5.6 hPa and is high in winter between 1.8 and 0.1 hPa. Seasonal variations of mixing ratio appear to show biennial variations between 1. and 0.1 hPa and semiannual variations above 0.032 hPa, though the period of observations is not long enough to get a definite conclusion. O3 mixing ratio above 0.032 hPa appears to be high from March to April and from October to November.¿ 1997 American Geophysical Union