The Widespread and most abundant grasses are Miscanthus sinensis and Pteridium aquilinum in the grassland of Cheju-Island. The vascular flora of the grassland are composed of 127 species in all. Those communities of Miscanthus sinensis Pteridium aquilinum Imperata cylindrica Themeda japon-ica and Zoysia japonica are relatively homogeneous. Standing crops of the mixed grass communities range from 657 g /$m^2$ to 2, 975 g /$m^2$ on August 30, and the value of daily net production is around 2.6~121 g/$m^2$. The standing crop of north facing slop showed higher than that of south facing slop. Relationship between the standing crop and water content, organic matter, total nitrogen and available phosphorus of soils in Cheju-Island showed high level of significant. Key words: Primary productivity, Cheju-Island