The equilibrium volatilities and solvent-polymer interaction indices are measured for 23 solvents in molten polysulfone. On the basis of the results, the solvents are ranked in the order of their effectiveness: phenol, pyridine, N-methylpyrrolidone, dimethylacetamide, methylene chloride, cyclohexanone, chlorobenzene, dimethylformamide, fluorobenzene, diglyme, toluene, xylene, chloroform, sulfolane, methyl ethyl ketone, acetonitrile, methanol, ethanol, carbon tetrachloride, dmethyl sulfoxide, decane, octane, and heptane. In determining the solvency power, the basic interpretative concept is that a large value of the Flory-Huggins interaction parameter indicates an unfavorable interaction, a low positive value indicates slightly favorable interaction, and a negative value indicates a rather strong specific interaction. Two other interaction indices, namely, the exchange energy parameter of Flory, X l z , and x*, the Flory-Huggins interaction parameter based on an hypothetical characteristic state, do not yield the same order as listed above. The data presented permits calculation of Henry's law constant and equilibrium volatilities at the temperature range of 25&30O0C, a processing range for polysulfone.