Dipropylamine is one of the promising antisolvents for extractive salt crystallization, but its solubility in water and phase equilibria in its aqueous solutions over a wide temperature range has not been studied in detail until now. The review of the literature shows that the water-dipropylamine system is classified as a self-separating system with a lower critical solution temperature (LCST). We used the visual-polythermal method in a –25–90°C range to study phase equilibria in the binary system water-dipropylamine and to plot the phase diagram of the system. A detailed study of phase states has revealed that the separation below –1.9°C takes place in overcooled mixtures of water and dipropylamine, i.e. it is nonequilibrium. On the part of the binodal curve that is in the metastable region, the coordinates of the lower critical solution temperature were evaluated by the phase volume ratio method: LCST = –4.7°С, 27.2 wt.% of dipropylamine. It was established for the first time that a non-invariant monotectic equilibrium takes place in the system at –1.9°C, whose solid phase is ice crystals. It was found for the first time that water and dipropylamine form the compound 2(C3H7)2NH·H2O congruent melting at –15.6°C. At –20.4°C, the system has a eutectic equilibrium, whose solid phases are ice and the chemical compound 2(C3H7)2NH·H2O.