The dissociation constant of picric acid in nitrobenzene, pK a =6.63, was established spectrophotometrically, and the standardization of potentiometric systems in this medium using picric acid titration is proposed as a standard method. The acid-base equilibria of a series of bases in nitrobenzene were also studied. The pK H B + values of the protonated bases of various structure were determined and compared with the pK H B + values in water and acetonitrile in order to evaluate the resolution of acid strength in these media.