The purpose of the present invention is to provide a nattō that has adequate quality as nattō and has markedly improved shelf life without degrading the quality thereof, and also to provide a method for manufacturing such nattō. Provided are: a method for manufacturing a nattō with improved shelf life, the method being characterized in that in manufacturing the nattō, steamed soybeans or boiled soybeans are inoculated with nattō bacteria and, after the soybeans are fermented in a temperature range of 37-53°C, a heating process is applied in which the temperature of the soybeans is maintained in a temperature range of 54-67°C for 3.5 hours or less and a nattō that is manufactured by such process and that is characterized by satisfying two conditions immediately following the heat treatment, which are (A) the free amino acid content is no more than 14.5 milligrams per gram of nattō and (B) The γ-PGA content is greater than 1.1 milligrams per gram of nattō.
