Abstract: RAPD molecular-marker technique was used to detect the genetic diversity among 18 ryegrass germplasms.Their genomic DNA were tested with RAPD using 26 10-mer primers screened from 110 arbitrary 10-mer primers.A total of 197 RAPD bands were obtained,in which 187 were polymorphic.The average percentage of polymorphic bands was 94.9%.The variation range of genetic distances was from 0 to 0.846 7.By a UPGMA cluster analysis on the RAPD molecular-markers,these ryegrass varieties were divided into three groups:(1) Yatsyn,Tetragold,Pandora,Abundant,Angus,Italian Ryegrass,Barwoltra,Normal Annual Ryegrass,Green Spirit,Normal Diploid and Triticale;(2) Peak,Cailente,Pinnacle,Primer and Bright Star;and(3) Dong Mu 70.