Experimental Solubilities of clonazepam, diazepam, lamotrigine, and phenobarbital in binary solvent mixtures of N-methyl-2-pyrrolidone (NMP) + water at 298.2 K were reported. The solubility of clonazepam, diazepam, and lamotrigine was increased with the addition of NMP, and maximum values are in neat NMP. The solubility of phenobarbital was increased with addition of NMP, reached the maximum value, and then decreased with further increase in NMP concentration. The Jouyban-Acree model was fitted to the results of these measurements, and solubilities were back-calculated by employing the solubility data in monosolvents in which the overall mean deviation of the models was 10.7 %.