Different methods of thermal stability determinations are reviewed. The process of thermal decomposition of aliphatic alcohols and their aqueous mixtures in the range of temperatures 583.15–663.15 K was studied using the method of isothermal pressure increasing in a closed system. The decomposition points (Td) alcohols dissolved in water are obtained depending on their concentration. The changes of thermal coefficients (isothermal coefficient of compressibility kT, coefficient of cubical expansion α and thermal coefficient of pressure β) and main thermodynamic properties (Cv, Cp, H, S, U, F, G) of studied mixtures depending on isothermal pressure increasing during the thermal decomposition of alcohols were calculated.