Equilibria data for the NaOH-Na2CrO4-Na2CO3-H2O quaternary system at (40, 60, and 80) degrees C were measured, and the phase diagrams at (80 and 40) degrees C were constructed. Furthermore, the crystallization areas in the phase diagrams are discussed in detail. In addition, the solubility of Na2CrO4 in NaOH solutions was compared with that in Na2CO3 saturated NaOH solutions, and the solubility of Na2CO3 in NaOH solutions was also compared with that in Na2CrO4 saturated NaOH solutions. On the basis of the phase diagrams, a strategy for effective separation of Na2CO3 from the NaOH-Na2CrO4-Na2CO3-H2O quaternary system has been proposed.