This study was conducted to identify the soluble carbohydrates in soybean seeds using on-line HPLC-RID-ES/MS and HPLC behavior, and to deter­mine their contents for high quality soybean breeding. The monosaccharide (glucose) and three oligosaccharides (sucrose, raffinose, and stachyose) were identified in Korean soybeans by their chromatographic behavior and results of on-line HPLC-RID-MS with Electro­spray Ionization mode. On the basis of HPLC with a RID detector, the 32 Korean major soybeans contain 0.37~pm0.26~% glucose, 4.55~pm0.91~% sucrose, 1.19~pm0.19~% raffinose, and 2.72~pm0.37~% stachyose on a dry basis. In 468 soybean germplasms, the ranges of glucose, sucrose, raffinose, and stachyose were 0.03 - 0.98~% , 2.33 - 6.96~% , 0.08 -1.87~% and 0.75 - 3.18~% , respectively. Among 500 soybean samples, oligosaccharide contents of 32 Korean major cultivated soybeans and 468 soybean germplasms were varied 5.83 - 10.06~% and 3.66 - 10.32~% , respectively. The composition of glucose, sucrose, raffinose, and stachyose in soluble carbo­hydrates of 500 soybean samples were 2.07 ~pm 1.75~% , 58.01~pm5.82~% , 10.13~pm2.28~% and 29.80~pm4.54~% , respectively. Sucrose appeared to be most prevalent in soy­bean soluble carbohydrates.