Using a laser monitoring observation technique, the solubilities of 7-aminocephalosporanic acid (7-ACA) in binary acetone + water solvent mixtures were determined from 274.45 to 301.15 K, which are the important data for the operation of the crystallization process of 7-ACA from its aqueous solution. The experimental results show that the solubility of 7-ACA increases slowly with the increase of the temperature and decreases sharply with the increase of the acetone concentration. The solubility data were fitted with both the Redlich-Kister equation and the λ h equation, and the correlative parameters were estimated by linear and nonlinear least-squares regression methods, respectively. It was found that the λ h equation can correlate with the experimental data very well. The parameters λ, h, and T-m1 were expressed as a function of the acetone volume concentration. The solubilities of 7-ACA in water and an acetone-water mixture can be calculated by interpolation with acceptable precision for an industrial application.