After a field experiment on loess soil, established for the purpose of the assessment of the effect of mineral fertilization on timothy grass yield, we have found that increase in nitrogen and, to lesser extent, in potassium fertilization significantly improved both fresh and dry matter yields. Mineral fertilization (NPK) has not caused any significant changes in the percentage contents of dry matter in the sward of this plant, however in its consequence certain tendencies and noticeable differences occurred. Increase in nitrogen and, to lesser extent, potassium fertilization caused a decline, and phos-phorus fertilization an increase, in the percentage contents of dry mater in the sward of timothy-grass.