Field experiments were carried out in 1951 to determine the effect of nitrogen fertilizer on the sex expression of hemp plants on the alluvial soil of Hongchow, Chekiang. Ammonium sulfate was used as the nitrogen fertilizer in the following quantities: 0 kgs., 50 kgs., 125 kgs., and 250 kgs. per Mou. It, one series of experiment, compost was added to each of the treatments mentioned above. The amount of compost used was 1500 kgs. per Mou. The chief morphological characters, total nitrogen contents and the percentages of female and male plants were studied and the results are summarized as follows: 1. The height and diameter of stem, leaf area and the number of branches in both female and male plants were increased with the increase of nitrogen fertilizer, but the response of female plants was more significant. The length/width ratio of leaves of the male plants was greater than that of the female. 2.The percentage of female plants was increased by the addition of nitrogen fertilizer and the increase was proportional to the amount of fertilizer used. However, the percentage of male plants was decreased by the same treatment. The results are given in the following table: 3.The amount of total nitrogen in the leaves was different in male and female plants. Before the flowering stage, the female plants contained more nitrogen than the male plants; while at the stage of fruiting, the result was just the reverse. This is probably due to the transference of nitrogen from the leaves to the reproductive organ. The amount of total nitrogen in the leaves was increased with the growth and development of both male and female plants, how ever, the maximum was reached at the stage before blossoming and then decreased with the maturation of the plants.