The results of a QSPR study of the toxicity of carboxylic acids in aqueous solution are reported. The molecular set comprises 35 carboxylic acids with the corresponding pK; a values in water. The set of molecular and topological parameters includes electrotopological state of the carboxy and methyl groups, molar refractivity, refractive index, n-octanol-water partition coefficient logKo/w, surface tension, and polarizability. Quite reasonable estimates are obtained, which improve the results of previous theoretical calculations.