Katsuwobushi is a dried product made from bonito meat by boiling, smoking, sun-drying and moulding processes and used for stock. The effects of these processes were investigated by analyzing the extractives of the each step product, especially free amino acids from the view point of its taste. The change of the contents of moisture, total-N, extractive-N and α-amino-N during the process is listed in Table 1 and that of free amino acids determined by the column chromatographic method using an ion exchange resing in Table 2. The extracts of the raw material reveal a very high value of histidine which occupies about 80% of total free amino acids. The content of taurine, lysine and alanine is also found to be comparatively high, whereas aspartic acid, cystine, tryptophan and arginine are not detected. A portion of each amino acid is lost in the boiling process. During the smoking process, some amino acids increase slightly, others remain almost unchanged, but most of the amino acids decrease again in the course of moulding, perhaps in its earlier stage, judging from the changes of amino-N and histidine. There have been some discrepancies among the reports on the change of free amino acids in the moulding process, but the present results do not support the opinion than the flavour of Katsuwobushi is improved by the increase of some amino acids due to the moulding. Trimethylamine oxide disappears in the course of processing and is found to have nc connection with the flavour.