Submergence is a major environmental stress that limits turfgrass growth and development. The objective of this study was to examine physiological and genetic variations in submergence tolerance of diverse perennial ryegrass (Lolium perenne L.) accessions. Two experiments (Exp 1 and Exp 2) were conducted for examining submergence tolerance of 99 perennial ryegrass accessions in a greenhouse for 7 days, respectively. Large variations in phenotypic traits such as color, plant height, relative growth rate (RGR, g^-1day) were observed both in the well-drained and submerged plants for two experiments. Under the well-drained and submerged conditions, RGR ranged from 0.0026 to 0.041 and from 0.0037 to 0.033 in Exp 1, and from 0.0026 to 0.041 and from 0.0037 to 0.033 in Exp 2, respectively. Variations in total water-soluble carbohydrate (WSC), fructan and sucrose concentration are being analyzed. The results indicate that variations in physiological responses of perennial ryegrass germplasm to submergence are valuable for cultivar improvement.