Before harvesting, one-time foliar fertilization of a mixture of fodder grasses (Lolium perenne, Phleum pratense, Festuca rubra, Festuca pratensis) was applied with selenium in doses of 5, 10, 15 and 20 g · ha –1 . The grasses were gathered three times, each time weighing the green mass and determining the Se content in dry matter. Selenium in doses ≤ 20 g · ha –1 did not significantly increase the yield. No selenium was detected in the dry matter of plants from the control sample and plants fertilized with Se in doses of 5 and 10 g · ha –1 . The dose of 15 g · ha –1 increased the Se content to 0.08 ±0.02 in the first harvest and to 0.02 ±0.03 mg · kg DM –1 in the second harvest. Se in the dose of 20 g · ha –1 increased the content of this element to 0.18 ±0.08 in the first harvest and to 0.07 ±0.02 mg · kg DM –1 in the second harvest. Selenium was not detected in the third harvest. The determined Se content in any of the fertilization doses was not sufficient to meet the needs of cattle. It is proposed to increase the dose of selenium and carry out three applications (before the first mowing, after the first mowing and after the second mowing) to improve the fertilization effect.