This paper discusses the measurement results of atmospheric attenuation at 11 and 18 GHz obtained by a dual frequency sun-tracker. The performance of the sun-tracker and the measuring method of atmospheric attenuation by means of observating the solar radiation are described. The annual, seasonal and monthly variations of measured atmospheric attenuation for each frequency are clarified based on a statistical analysis of data measured over a period which continued for three years. As an outcome of the regression analysis concerning the relation between the measured atmospheric attenuation and the surface meteorological data, two models were obtained. The first gave rise to a single linear equation which has the water vapor density as a variable. The second model took into account the oxygen density as well as the water vapor density. Moreover, the precision of estimation which can be achieved in estimating the atmospheric attenuation from the surface meteorological data using these models was shown.