To help the development of separation technology for the mixture of 3-chlorophthalic anhydride and 4-chlorophthalic anhydride, the solubility data of 3-chlorophthalic anhydride and 4-chlorophthalic anhydride in tert-amyl alcohol, carbon tetrachloride, cyclohexane, methanol, methyl acetate, and acetonitrile were measured in the temperature range of 283.15 K to 328.15 K by a static method. It was shown that the solubilities of both 3-chlorophthalic anhydride and 4-chlorophthalic anhydride increased with the increase of temperature. The experimental solubility data in six pure solvents were correlated by the modified Apelblat equation, the van't Hoff equation, the lambda h (Buchowski) equation, and the NRTL model, among which the modified Apelblat equation can give better correlation results than other models. In addition, the dissolution thermodynamic properties, including enthalpy, entropy, and Gibbs energy were determined. The experimental data would be of great significance for the design and optimization of the crystallization processes of 3-chlorophthalic anhydride and 4-chlorophthalic anhydride.