The present invention relates to a method for the production of a stable biodegradable, high water absorbable .gamma.-polyglutamic acid (.gamma.-PGA) hydrogel by directly cross-linking (A) a .gamma.-polyglutamic acid (.gamma.-PGA), a .gamma.-polyglutamate, or a mixture thereof, and optionally a polysaccharide containing a carboxylic and/or carboxylate group, an amino acid, or a mixture thereof; and/or (B) a microbial culture broth containing a .gamma.-polyglutamic acid (.gamma.-PGA), a .gamma.-polyglutamate, or a mixture thereof, and optionally a polysaccharide containing a carboxylic and/or carboxylate group, an amino acid, or a mixture thereof, with a cross-linker comprising a compound having three or more functional groups or a mixture of a compound having three or more functional groups and a compound having two functional groups, wherein each of the functional groups can react with a carboxylic group (--COOH), carboxylate group (--COO.sup.-), aldehyde group (--CHO), hydroxyl (--OH), carbonyl group (--CO), sulfone group (--SO.sub.2), amino group (--NH.sub.2) or nitro group (--NO.sub.2), or a mixture thereof. The present invention further relates to a stable biodegradable, high water absorbable .gamma.-polyglutamic acid (.gamma.-PGA) hydrogel and its uses.