Radioactive substances have a number of features which can be explained by the effect of selfirradiation. Systems containing radioactive elements are in a nonequilibrium state. The fraction of particles (molecules, atoms, ions) having increased energy exceeds the equilibrium value in these systems. The regions of the substance in which there is retardation of the ex- and ß-particles and the recoil atoms have a higher concentration than the equilibrium value of structure defects and increased free energy. These factors should affect the vapor pressure, solubility, dissociation pressure, equilibrium constants of chemical reactions, reactivity, specific heat, density, electrical conductivity, thermal conductivity and other properties of radioactive substances and also the character of their phase transformations. From this point of view a study is made of literature data on some properties of various radioactive substances.