The objective of this experiment was to determine the hydrocyanic acid (HCN) levels that have poisonous effects on animals, in 4 different sorghum and 1 sudangrass species, which were developed by Batı Akdeniz Agricultural Research Institute and widely used in our country. Experiments were carried out in experimental fields of institute during 2014 and 2015 growing seasons. Rox, Leoti, Early Sumac and Nes sorghum varieties with Gozde 80 sudangrass variety were cultivated as May-June and June-July planted crops in a randomized block design with three replications. Plants were harvested when they reached 40, 80 and 120 cm heights and they were extracted in order to determine HCN contents. The analysis of variance indicated that there were significant differences in terms of HCN content in all varieties. The HCN levels of varieties were determined in Gozde 80, Early Sumac, Nes, Leoti and Rox in descending order. In the first year, the highest HCN level was determined in Early Sumac variety with 40 cm harvesting height at the first sowing time, the lowest level was determined in Gozde 80 variety with 120 cm harvesting height at the second sowing time. In the second year, the highest HCN level was determined in Gozde 80 variety with 40 cm harvesting height at the first sowing time, the lowest HCN level was determined in Early Sumac variety with 120 cm harvesting height at the second sowing time. At the end of the experiment, the highest HCN content was found at the first sowing time with 40 cm harvesting height.