In order to study the change of nitrogeneous compounds during the "Natto" preparation, the contents of insoluble protein, water soluble protein and amino nitrogen were determined and the pattern of peptides and amino acids was investigated by paper chromatography for the fractions resulting from molecular sieving. The results are summarized as follows: 1. Insoluble protein nitrogen which was increased to 84% by autoclaving the native soybean decreased to 44%, whereas the trichloroacetic acid soluble nitrogen increased from 8% to 45% during Natto preparation, But the soluble protein nitrogen showed a slight increase. 2. Fractionation of the peptides using Dowex-50 resins showed that they consisted mostly of lower molecular weight peptides which increased in accordance with the progress of fermentation, especially after 30-hour period. 3. Sixteen known and two unknown amino acids, and three peptides with different Rf values were identified during the Natto preparation. Their appearance showed some difference in that phenylalanine appeared after 10 hours, methionine, after 20 hours and proline, after 30 hours, respectively. The three peptides appeared at the different stage of fermentation.