Phase equilibria in the water–butyric acid binary system in the range of −10÷0° C and in the sodium chloride–water–butyric acid ternary system in the range of 10.0÷60.0° C were studied using the visual polythermal method. The phase diagram of the water–butyric acid binary system at −9.5° C is characterized by eutectic equilibrium, the solid phases of which being ice and butyric acid crystals. The metastable delamination range was found on the ice crystallization field, bounded by a binodal curve with an upper critical solution temperature of −3.7° C.