The functions of organs in young soybean seedling were determined by means of proteomic analysis. Extracts from leaves, hypocotyls, and roots were separated by two-dimensional polyacrylamide gel electrophoresis, and the proteins were identified by mass spectrometry and protein sequencing. The identified proteins were categorized into various groups according to their function. The leaf was abundant in proteins associated with energy production (50.0%), the hypocotyl was rich in defense proteins (31.8%), and the root contained defense-related proteins (16.7%) and destination and storage proteins (26.7%). Stem 31-kDa glycoprotein, 20 kDa chaperonin, 50S ribosomal protein, and trypsin inhibitor were common to all three tissues. The sequence information obtained from the soybean proteome should be helpful in predicting the functions of unknown proteins.