The influence of γ-irradiation on D – and L-glucose, D – and L-galactose, D – and L-mannose was examined in the solid polycrystalline state. Hydrogen was the principal gas product of radiolysis of hexoses. Radiation yield (G) of H₂ changed from 2.2 for galactose to 3.2 (1/100 eV) for glucose and mannose. The ESR spectra of radicals formed in irradiated hexoses were similar and indicated the presence of secondary radical mixture. Integral G-value of radicals decreased with dose. Process of radical disappearance could be described with equations of polychronic kinetics. Radiation stability of galactose was one and a half times higher, than radiation stability of glucose and mannose. This fact rationalised essential contribution of the C₄-H bond breaking process in formation of radical products and H₂. Radiation stability of D – and L-isomers of monosaccharides under non-polarised irradiation was identical. Radicals formed in irradiated monosaccharides lived at room temperatures for several months and it should be taken into account on application of radiation-sterilized pills.