The Solubility of isophthalic acid in propyl acetate and the partition coefficient between propyl acetate and water were measured in the temperature range from (303.2 to 363.2) K. The effect of composition on the partition coefficient was also investigated. The results showed that the changes of the initial concentration of isophthalic acid in the mixtures had a remarkable effect on the partition coefficient. The experimental solubility data were fitted by a logarithmic formula, and the experimental partition coefficient data were correlated with the NRTL activity coefficient model. The calculated results showed good agreement with the experimental data.