This experiment was conducted to study the factors related with yield components in 5 varieties of perennial ryegrass and was surveyed for the biological yields(BY). shoot weight(SHW). root weight (RW), leaf weight(LW), stem weight(SW), plant length(PL), leaf area(LA), number of tillcr per plant (NT), root lcngth(RL), shoot and root ratio(S/R), ratio of root length and weight(RL/RW) and weight of a tiller(WT) in autumn growth stage. These results are summarized as follows;1. The yield components were varied during the stage of growth and in relation to the varieties in autumn. 2. The yield is consisted of 73 % by shoot and 27% by root in autumn.3. The varieties of the highest biological yields were Tempo, Maprima and the lowest biological yields were P-2, Caliente in autumn. 4. The variety of Tempo was largely affected by the factors of shoot weight, root weight, ratio of root length and weight, and weight of a tiller. but the variety of Caliente was influenced by the factors of leaf weight. stem weight, leaf area, SIR ratio and weight of a tiller on the yield. 5. The highest biological yields was obtained at the time of 4~5th(10/4~1018) and the lowest yield was showed at the time of 3~4th(9/30~1014) in autumn. 6. The time of the highest biological yields were resulted that the variety of Tempo was obtained between the time of 5~6th. Maprima was obtained between the time of 1~2nd and the varieties of Manhattan, P-2, Caliente were obtained between the time of 4~5th on the stages of growth in autumn.