The solubility and density of the equilibrium liquid phase for the ternary K2C2O4 + H2O2 + H2O system were determined experimentally at (283.15 and 293.15) K. The phase diagrams of the system were constructed based on the measured solubility. The compound K2C2O4 center dot H2O2 was confirmed by Schreinemaker's wet residues method. At (283.15 and 293.15) K, two solid phases were formed in the ternary K2C2O4 + H2O2 + H2O system that correspond to K2C2O4 center dot H2O and K2C2O4 center dot H2O2. Results indicated that the phase diagrams of the ternary system are similar at different temperatures. The double salt K2C2O4 center dot H2O2 has a bigger crystallization field than either K2C2O4 center dot H2O or the mixture. The solubilities of K2C2O4 center dot H2O and K2C2O4 center dot H2O2 increase slightly with increasing temperature, while the crystalline region of the compound K2C2O4 center dot H2O2 decreases as the temperature increases.