Abstract: Cucumber seedlings under room condition are placed 120 cm under 40 watts of ultraviolet light (UV-C, <280 nm) and irradiated totally 10, 5 or 4 times during the whole seedling stage (in 2, 4 or 6 days intervals, respectively) for 10 min each time. The results show that plant height, stem width, top weight and root weight all decrease with the increase of irradiation times. It has little effects on photosynthetic pigment content in leaves. The photosynthesis, stomatal conductance, intercellular CO2 concentration and water use efficiency remarkably decease under UV-C irradiation, while evaporation remains normal.