The results of comprehensive studies of transformation of hydrocarbons in light catalytic gasoil (LCG) by ozone in different ozonation conditions are reported. It was found that low-temperature oxidative cracking and oxidative polycondensation reactions take place as a result of electrophilic 1,3-addition of ozone to the components of the LCG. The flash point of the samples decreased, and the concentration of adsorption resins increased. Olefins have the highest activity in interaction with ozone. The optimum conditions of ozonation of LCG were selected.