The cucumbers were grown in three kinds of nutrient* 150 ppm NOj--N, 150 ppm NH-N, and the mixture of 75 ppm N03-N and 75 ppm NH4+-N, separately for seven days. The best and the worst growth were in the nutrient of NO-N and NH-N, respectively. Although they took the same amounts of combined nitrogen from each nutrient, the better assimilation of NO-N than NH-N in the cucumbers resulted in heavier dry weights, higher contents of total nitrogen, and higher soluble proteins contents in the leaves of cucumbers that grown in higher concentration of NOf-N. The compostions of soluble proteins in the leaves of cucumbers were also influenced by nitrogen sources by showing their discrete electrophoretic patterns.