Equilibrium solubility of sodiumsulfadiazine (Na.SDZ), sodiumsulfamerazine (Na.SMR), and sodiumsulfamethazine (Na.SMT),was determined in aqueous binary mixtures of propylene glycol (PG) at 298.15 K. If the solubility values expressed in both concentration scales are considered, i.e. mole fraction and molarity, in water-rich mixtures the solubility decrease as: Na.SDZ N Na.SMT N Na.SMR, whereas, in PG-rich mixtures the observed order is: Na.SMT N Na.SDZ N Na.SMR. In all cases the solubility in neat water is higher than those in neat PG. Correlation of the solubility data obtainedwasmade bymeans of the Jouyban–Acreemodel for all the sodiumsulfonamides. Otherwise, apparent specific volumes (ϕVsp) of sodiumsulfonamides at saturationwere also calculated in all the mixtures. The average ϕV sp values are as follows: 0.663 cm3 g−1 for Na.SDZ, 0.723 cm3 g−1 for Na.SMR,and 0.740 cm3 g−1 for Na.SMT, with a variation lower than 5.0% in each case.