This study was carried out to make clear the influences of light and temperature conditions on the effect of Ethrel-spray on cucumber seedling. Seedlings, which were germinated at 30℃ in darkness and grown 3-4 cm in hypocotyl length, were grown at 25℃ for 12-15 days under several light and temperature conditions after sprayed with Ethrel solution. In the artificial light room (5,000 lux), the hypocotyl elongation of seedlings which were sprayed with 50 or 100 ppm solutions was greater than that of control (0 ppm) in 16 and 24 hours of photoperiods. In low light intensity (300 lux), the hypocotyl elongation of treated seedlings was smaller than that of control. At 20, 25 and 30℃, the elongation of the treated ones was the same as that of control. When Ethrel solution was sprayed soon after transplanting and seedlings were grown in blue and red fluorescent lights, the elongation of the 50 ppm Ethrel-sprayed seedlings was greater than that of control throughout the experiment regardless of light quality and light intensity. On the other plots of Ethrel treatment, there were at first observed various rates of growth inhibition in hypocotyl. The inhibition decreased gradually with the passage of days. In high light intensity of blue light, the final elongation of the 100 or 200 ppm Ethrel-sprayed seedlings was greater than that of control. When 100 ppm Ethrel solution was sprayed on seedlings 24 hours after transplanting, the promotive effect in hypocotyl elongation was observed in low intensity of red and high intensity of blue lights.