Dew is one of the important water sources for plants growing, especially in arid and semi-arid regions. However, it was seldom researched. The dew amount and its relationships with input-output of water resources in the jujube plantations in semi-arid Loess hilly-gully region were investigated during jujube growth periods in 2012 and 2013, depending on the dew intensities, canopy temperature, canopy relative humidity, sap flow, soil moisture and meteorological factors which were measured by the dielectric leaf wetness sensor (LWS), the VP-3 relative humidity/temperature sensor, thermal diffuse probe (TDP), neutron probe and meteorological station, respectively. The results showed that the dew amount increased throughout the jujube growth seasons and reached its maximum value at the fruit ripening stage. The cumulative dew amounts during jujube growth periods in 2012 and 2013 were 31.31 mm and 37.87 mm，respectively, which accounted for 6.87% and 7.90% of rain, 10.00% and 15.00% of transpiration, and 17.65% and 17.90% of evaporation at the same period, respectively. The dew amount with high frequency and strong stability had a large proportion of heavy dew in the jujube plantations in the Loess hilly-gully region. As one of the input water resources, dew significantly reduced jujube transpiration during fruit enlargement and ripening stages (P<0.05), but had no significant effect on evaporation. It is indicated that dew is an important part of water resource which affects regional water balance in the jujube plantations in semi-arid Loess hilly-gully region and it should not be ignored.