Gamma-glutamyl hydrolase with a molecular mass of 28 kDa was purified from the culture broth of Bacillus sp. isolated from Thai Thua-nao, a natto-like fermented soybean food. The purified enzyme hydrolyzed chemically synthesized oligo-gamma-L-glutamates but not oligo-gamma-D-glutamates and degraded gamma-polyglutamic acid to a hydrolyzed product of only about 20 kDa (with D- and L-glutamic acid in a ratio of 70:30), suggesting that the enzyme is a gamma-glutamyl hydrolase that cleaves the gamma-glutamyl linkage between L- and L-glutamic acid of gamma-polyglutamic acid.