Growth of sorghum and maize was analysed to determine the synthesis and accumulation pattern of reserved carbohydrates and its relationship to net energy value of the plants. The experimental fields were laid down as a randomized block with 4 replications at Livestock Experiment Station in Suweon from 1984 to 1986. The results are summarized as follows: 1. Concentration of non-structural carbohydrates was associated with increasing of assimilable leaf area (P≤0.1%). TNC accumulation was occurred rapidly from the growing point differentiation and. it showed the highest content at soft dough with a value of 16.73% in sorghum and 29.51% in maize. During the maturity, TNC was declined comparatively as the starch increased. 2. Non-structural carbohydrates was mainly accumulated as mono-and disaccharose both in sorghum and maize. Mono-and disaccharose was decreased when the temperature exceeded. 28/18℃ (day/night), while structural carbohydrates, especially cellulose and other cell-wall constituents increased. 3. Digestible dry matter content in sorghum was decreased from 81.1% at 3-leaf stage to 58.5% at maturity. But DDM in maize was less changeable in the whole vegetative development. 4. Net energy value showed linear response to the synthesis and accumulation of reserved carbohydrates. Net energy for lactation (NEL) in maize was increased during the maturity and it reachad maximum at physiological maturity. However, the increment of NEL value in sorghum was not noticeable.