The aim of study was to evaluate serradella yielding cultivated as undersown crop in rye (Secale) or spelt wheat (Triticum aestivum ssp. spelta L.) harvested in milk-dough stage and complete maturity in ecological farm. The study was carried out in 2011 in individual farm in Włodawa region (lubelskie province) and in 2012 at Agricultural Advisory Center in Szepietowo (podlaskie province). The trial was conducted in split-plot terms with control objects, in four replications. In trials with winter cereals following objects have been compared: control – rye – sowing without serradella, control – spelt wheat – sowing without serradella. In the scheme of experiment two factors were included. Cereal species: rye and spelt wheat were the first experimental factor. Terms of cover crop harvesting: milk-dough stage and complete maturity (on grain) were the other factor. Yield of serradella harvested in autumn was significantly differentiated depending on term of cover crop harvesting as well as cereal species, in which was sown. It was noted almost two times greater yield of stubble sown in cereals harvested in milk-dough stage period than those harvested in complete maturity. Moreover a higher level of yield was obtained from serradella sown in rye than serradella sown in spelt wheat. Lower amount of precipitation in July, especially after harvesting of the cover crops caused desiccating of serradella plants sown in spelt wheat and yields of serradella sown in rye were relatively low. Undersown crop of serradella in cereals had positive influence on dry matter yields of rye and spelt wheat harvested in milk-dough stage. The yielding level of rye in pure sowing was significantly greater than spelt wheat one. However yield of rye with undersown crop of serradella was greater only in more wet year. In year of limited amount of precipitation spelt wheat cultivation ensured obtaining a greater yield of grain irrespective of the sowing method. However, better yielding of rye was noted in year of greater amount of precipitation. In 2011 undersown crop of serradella in cereals had no influence on yielding level of cereal, however in second year (2012) had low influence on spelt wheat and decreased yield of rye.