AbstractAn oat‐pea (Arena sativa L.‐Pisum arvense L.) forage mixture was sampled at nine successive stages of growth during 3 consecutive crop years. Samples were separated into oat and pea components for chemical analyses and yield determinations. Percent dry matter in both crops and nitrogen‐free extract (N.F.E.) in oats increased during the growing season. Percent N.F.E. in peas, Ca in oats, and fat, Mg, and P in both oats and peas remained relatively constant during the sampling period. Percent crude fiber increased in both crops until oats were in the early milk stage and peas had 3 to 4 pods per plant and then declined in both crops. Percent ash and K in both crops and percent Ca in peas declined throughout the sampling period.Percent crude protein decreased rapidly in both crops during the first two sampling intervals, then declined slowly in oats, and increased slightly in peas during subsequent growth.Oats were higher than peas in percent dry matter, fiber, ash, and K. Levels of N.F.E., fat, and P were quite similar in the two crops, except that oats were lower than peas in N.F.E. during the first two samplings. Peas were higher than oats in percent protein, Ca, and Mg, except with the first two samplings when oats surpassed peas in percent protein.Rate of dry‐matter accumulation was higher for oats during the first half of the sampling period but higher for peas during the last half. Per‐hectare yields of dry matter and of the various chemical constituents at conventional harvest stage revealed that oats and peas were complementary in composition. Oats surpassed peas in per‐hectare yields of dry matter, fiber, ash, N.F.E., and K. Peas, however, contributed most of the protein, Ca, and Mg. Oats and peas were about equal in yield of fat and P.