On the ground of bibliography in this paper were presented numerous results of investigations on the point of Lolium perenne occurrence in Poland, in the sward of permanent grassland in Poland, according to the natural and anthropogenie factors. Lolium perenne was of frequent occurrence in Poland in the different habitats of permanent grasslands. The most favorable conditions Lolium perenne finding in the low pastures sward of Lolio-Cynosuretum association and in the excessively treaded down sward of Lolio-Plantaginetum association. The main factors reducing the oceurrence of Lolium perenne sward of permanent grassland are: low temperatures of air (especially in the early-spring period), excess or indigence of water in the soil, excess or indigence of elements in the soil, mowing use or excessive grazing, in the mountain altitude of 700 m a.s.l. and high rivalry of concurrent species.