A technique for highly efficient production of γ-amino butyric acid (GABA) using mochi barley of the group of mules barley, as a raw material. The technique converts glutamic acid into GABA due to the glutamate decarboxylase contained in the mochi barley so GABA-mochi barley grains and GABA-mochi barley bran and GABA-containing bran supernatant can be produced highly-efficiently by mixing mochi barley grains, which have been polished in a barley milling device to an extent of 2% or more and less than 20%, with a glutamic acid solution, which has a concentration of 0.1 to 3% and a pH value of 2 to 9, and soaking the barley in the solution at room temperature for 1 hour or more to overnight or, after soaking in the solution similarly for 1 hour or more to overnight, draining the barley grains, and keeping it overnight at room temperature.
