Eight forages (alfalfa, birdsfoot trefoil, red clover, bromegrass, orchardgrass, perennial ryegrass, quackgrass, and timothy) at three maturities were evaluated for ruminal DM, CP, and NDF degradation kinetics. Duplicate dacron bags were incubated for 0, 3, 6, 10, 13, 25, 48, and 72 h in two late lactation Holstein cows fitted with ruminal cannulas over eight experimental periods. Species and maturity effects were observed for soluble, slow, and undegraded fractions; degradation rate; and ruminally degradable DM, CP, and NDF. Significant species by maturity interactions also were evident for fractions and ruminal degradabilities of DM, CP, and NDF. Legumes exhibited more extensive ruminal DM degradation than did grasses. No clear trends were evident in rate of ruminal CP degradation between legumes and grasses. Mature grasses were lowest in ruminally degradable CP. Legumes exhibited a higher undegraded fraction and faster degradation rate of slowly degraded NDF fractions, resulting in similar ruminally degraded NDF for legumes and grasses. Extensive differences in ruminal degradation kinetics existed between perennial legume and grass species and maturities. Species by maturity interactions were diverse, making categorization of degradation characteristics of legumes and grasses difficult.