Perennial ryegrass is one of the most important forage species in temperate regions throughout the world. This species is spread in north and west of Iran i.e. Alborz and Zagros Mountain rangelands. Because of the importance of Lolium perenne in grassland productivity any improvement in dry matter yield, would be very beneficial in terms of animal productivity. In order to study the genetic variation among local and foreign accessions/ varieties of perennial ryegrass in Natural Resource Gene Bank, and the study of ploidy x maturity interaction effects on dry matter yield, an experiment was conducted at Alborz Research Center, Karaj, Iran. Seedlings of 29 accessions/ varieties were transplanted in the field. Each row plot contains five spaced plants were established using a complete block design with three replications. Forage dry matter yield, basal cover, ear emergence date, pollination date, stem number, stem height and persistency were assessed in four harvesting dates.Significant differences were observed for all of the characters for each cut. For ear emergence date, there was 42 days interval between the earliest and the latest maturity accessions. Moy, Yatsyn and Syrachal were the earliest and, Carrick and Sarsfield were the latest varieties. For annual dry matter yield, Spega and Magician with more than 13 tons/hectare and Tivoly with 6.31 tons/hectare had the highest and the lowest forage dry matter yield respectively. There were also significant differences between cuts. Dry matter yield decreased over the seasons. The first cut had about 50 percent of total annual yield. In overall, tetraploids produced more dry matter yields than diploids. But, diploids had a high ratio of reproductive tillers that indicated their high potential of seed production. Estimates of broad sense heritability, although low, suggested that response to selection should be possible and recurrent selection based on progeny testing should be effective.