In order to prevent the poisoning of the hydrocyanic acid (HCN) in animals, the effect of nitrogen fertilization level on the content of HCN in a hybrid (Pioneer 988) of sorghum x Sudangrass was studied. Samples were taken in the growing days of 38th, 48th, 58th, 68th and 78th days after emergence and in the 1st (Jul. 6th), 2nd (Aug. 1st), 3rd (Sep. 1st) and 4th (Oct. 14th) cuttings. And the HCN content of 4-6 leaves from the top, and sheaths and stems joined to the 1st leaf blade from the top, and ears were determined in the fresh plane. The nitrogen fertilization did not affect on the HCN contents of the plants among the growing days or among the first growth and regrowth. Generally the HCN content of plants was decreased with the growth of plants, and the HCN content of the leaf blades and sheath was also lowered suddenly at the time which ears opened in 68th days after emergence, though a trend was shown to have higher value at 78th days comparing with those of 68th days in the plot fertilized 35㎏ of nitrogen. The 3rd or 4th leaf blade from the top contained higher HCN than those of others until 58th days after emergence, though the HCN contents were not found different among leaf blades, sheath and stems of the plants. The first leaf blade fertilized 35㎏ of nitrogen showed also a trend to contain more HCN comparing with those fertilized 15 and 25㎏ of nitrogen until 48th days after emergence. And the ears from plants fertilized 15㎏ of nitrogen showed a trend to have lower HCN than those fertilized more nitrogen. The effects of the first growth and regrowths on the HCN contents of the plants were not found, and the HCN contents of sheaths generally contained lower HCN than those of leaf blades and stems which had relatively similar values. Among leaf blades from the top in the 1st and 2nd cuttings, and second leaf blades from the top in the 3rd and 4th cuttings contained more HCN than those of other leaf blades. In the plot of 15 and 25㎏ of nitrogen fertilized, the stems had the highest HCN content among various parts of plants. But in the plot of 35㎏ nitrogen fertilized, the highest values were shown in the stem of the 1st cutting and in the 2nd or 3rd leaf blades of the 2nd, 3rd and 4th cuttings, and the HCN content of stems was decreased with the cutting date delayed.