(Solid + liquid) phase equilibrium (SLE) has been measured for 4-chloro-2-benzofuran-1,3-dione anhydride and 5-chloro-2-benzoluran-1,3-dione anhydride using differential scanning calorimetry (DSC) over the whole concentration range. It was found that this system is a simple eutectic system. The eutectic point is at T = 336.95 K and a mole fraction of 4-chloro-2-benzofuran-1,3-dione of 0.3482. Furthermore, the results obtained in mixtures of (4-chloro-2-benzofuran-1,3-dione and 5-chloro-2-benzofuran-1,3-dione) have been compared with those predicted by the ideal model and correlated by Wilson and nonrandom two-liquid (NRTL) equations. The best modeling results were obtained using the NRTL model with the average root-meansquare deviation of sigma = 7.88 K.