The solubility of 6-aminopenicillanic acid in aqueous solutions of various concentrations of sodium sulfate and ammonium sulfate was determined from (274.15 to 303.15) K at atmospheric pressure using a synthetic method. Results showed that sodium sulfate has a salting-in effect on the solubility of 6-aminopenicillanic acid; ammonium sulfate has a salting-in effect if its concentration is below 0.5 M and a salting-out effect if its concentration is above 0.5 M. The solubility data were accurately correlated by a semiempirical equation.