The rutin found within buckwheat, has bioactivities such as hypertension prevention and antioxidation among others. In this study, the usage of buckwheat in miso was investigated. The protease activity for buckwheat koji (malted buckwheat) was higher than for the general malted rice by comparison' The decomposition of the protein was fast for the miso using buckwheat koji, and many free amino acids were included and it had a distinctive flavor. The rutin which originates from the buckwheat transforms into quercetin, etc. in the miso. Buckwheat added to the miso enriched it with rutin, quercetin, and the saccharides that made the miso mild.