Growth of rye cv. Paldang and barley cv. Bunong were analysed to determine pattern of the Weender components and their influence on digestible dry matter and net energy accumulation of the plants associated with stage of morphological development. The experimental fields were laid down as a randomized block design with 4 replications from 1984 to 1986 at Livestock Experiment Station in Suweon. Concentrations of crude protein and crude fat were decreased as the growth of plants advanced. The highest accumulation of crude protein occurred with a synthesis rate of 5 ㎏ (barley) and 6.1㎏/10a (rye) at stage of growing point differentiation, when the plant showed a greatest enlargement of assimilable leaf area. Crude fibre as well as cell-wall constituents in the plants was increased markedly immediately, after the stage of growing point differentiation and it was the lowerest at stage of blooming. Cellulose was found to be a main component of the cell-wall constituents both in rye and barley. Value of net energy in rye and barley was decreased as the morphological development progressed and it was the lowest at stage of blooming by 4.98 and 5.03 MJ-NEL/㎏ dry matter. However, NEL value of barley increased during maturity of grain and it showed 5.16 MJ at soft dough and 5.32 MJ/㎏ at hard dough. NEL value of rye was still low at stage of maturity. The highest yields of net energy lactation were obtained at stage of soft dough in rye and stage of hard dough in barley with a value of 6345 MJ and 6331 MH/10a, respectively.