Observation of typhoon “Kalmaegi”（NO.0807） by using unmanned aerial vehicle (UAV) was carried out on 18 and 19 July, 2008 for the first time in China mainland. According to the UAV-observing data during the weakening process of typhoon to tropical storm on 19 July, 2008, some preliminary analysis was presented in this paper. The preliminary results show that: (1)the UAV′s cruising altitude was about 500 m and the nearest distance to the typhoon centre was about 100 km. All the meteorological elements data (temperature, relative humidity, pressure, wind direction, and wind speed) were obtained during observation period and the data acquisition rate exceeded 90%. (2)The average value of pressure was 949.1±9.7 hPa, and temperature was 24.2±1.3℃. (3)During the observation period, UAV was almost within the precipitation cloud, and the average of relative humidity was about (88.4±6.1)%. The preliminary analysis suggests that this model UAV has the capability to observe the typhoon boundary layer.