We analyzed the levels of free amino acids and related substances, and nucleic acid-related compounds in a niboshi extract soup stock and niboshi-flavored mixed seasoning soup stock by using an amino acid analyzer. Niboshi (30 g) was soaked in 1 l of water for periods of 0, 30, and 180 min. Each solution was boiled for 5 min and used to prepare the niboshi extract soup stocks. These soup stocks contained serine, 3-phospho-1-serine, taurine, threonine, aspartic acid, asparagine, glutamic acid, glutamine, glycine, alanine, valine, cysteine, methionine, cystathionine, isoleucine, leucine, tyrosine, tryptophan, phenylalanine, ornithine, lysine, histidine, arginine, hydroxyproline, proline, urea, NH3, and nucleic acidrelated compounds of ATP, ADP, AMP, IMP and HxR. The mole fraction of glutamic acid in the total amino acids and their related substances in the mixed seasoning soup stock was 95%. The only nucleic acid-related compound detected in the mixed seasoning soup stock was IMP. The glutamic acid content was over 11.8-fold higher in the mixed seasoning soup stock than in the niboshi extract soup stocks. The IMP content was over 2.9-fold higher in the niboshi extract soup stocks than in the mixed seasoning soup stock.