Abstract: In order to determine the characteristics of dew amount and its inducing factors in the semi-arid area of loess hilly region of China, a year-long in-situ monitoring experiment was carried out in Ansai County of Shaanxi Province, using a leaf wetness sensor (LWS). Results showed that the annual cumulative dew amount in Ansai area in the water year of 2015-2016 was 29.85 mm with a daily maximum of 0.82 mm. The amount of dew condensation manifested two strong characteristics: the daily and seasonal changes. The majority of daily dew amount appeared from 18:00 o’clock to 7:00 o’clock, and the seasonal dew changes showed that the maximum yield of dew occurred in the autumn, followed by the summer, with the least amount in spring and winter. With respect to spatial and temporal distribution, rain and dew were highly complementary as dew occurred mainly in the cloudless nights, but it was more conducive to dew condensation during the days right before and after the rain events. Relative air humidity and the difference between air temperature and dew point were the main factors influencing dew condensation. Dew amount was significantly positively correlated to relative humidity (r=0.726, P<0.01), and negatively correlated to air temperature-dew point difference (r=-0.725, P<0.01). Wind speed and direction affected dew condensation to some extent, but dew amount was weakly correlated to wind speed (r=0.133, P<0.01) and wind direction (r=0.219, P<0.01).