Starch hydrolizates were used to obtain sodium gluconate and calcium gluconate. In the process of bioconversion Aspergillus niger mutant J-O-12 was used. The medium containing starch hydroliza te was treated by glucoamylase and parallel A. niger was cultivated in this medium. A.niger converted formed glucose to gluconic acid. In the best experiments of bioconversion, obtained yields were close to stoichiometric values.