It was found that a bacterial strain, KN-69, which was isolated from soil, converted d-glucose to d-fructose. From the results of investigations of characters, it seems reasonable to conclude that the strain is related to Aerobacter cloacae Bergey et al. The formation of d-fructose in the glucose containing reaction system was confirmed by isolation and characterization of the product. Fructose formation from glucose by A. cloacae, strain KN-69 was investigated. The maximal activity appears to occur at about pH 8.0 and at 42~43°C. Starting either from glucose or fructose the equilibrium is reached when about 47~48% fructose is present in the reaction mixture. Isomerization activity of the cells depends on the carbon source in the culture medium, e.g. xylose grown cells react with glucose but not with other aldohexoses and cells grown on the hexose media do not react with those hexoses. Reagents such as carbon tetrachloride, toluene, and bromobenzene strongly accelerate fructose formation by washed living cells, while chloroform shows little effect.