A study was made on the accumulation of carbohydrates, total nitrogen, oil, fatty acids and dry matter in seeds of soybeans during development stage until maturity. The first sample was taken at 30 days after flowering of the cultivar Santa Rosa planted in a multiplication plot at the Experimental Station in Campinas. Subsequent sampling was done at intervals of seven days until maturity. The results showed that the greater part of the dry matter, total nitrogen and total polysaccharides accumulate during the interval between 37 and 65 days after flowering (DAF) and small increases thereafter. During the above mentioned interval the accumulation in the seed was: dry matter 3.92 to 71.40 mg, total nitrogen 0.32 to 7.39 mg and polysaccharides 0.73 to 14.25 mg. During the interval of 37 to 72 DAF there was greater accumulation of soluble sugars which varied from 0.33 to 19.95 mg/dry matter per seed whereas soluble polysaccharides in water accumulated during 51 and 82 DAF which varied from 0.52 to 2.16 mg/dry matter per seed. Most of the fatty acid accumulation took place during 51 and 65 DAF and varied from 4.3 to 15.6 mg/dry matter per seed. It was observed that the rate of the seed oil accumulation decreased during the rainny period and increased during the higher temperatures period. The accumulation of linoleic acid correlated with oil. A decrease in the saturated fatty acid contrary to the unsaturated fatty acid was observed during the development stage of the seed.