A simple and fast UV-Vis spectrophotometric method with high specificity, accuracy and precision for the quantification of PR in new topical nanoemulsions was developed and validated. The method is suitable for the quantification of PR content in nanoemulsions and determination of entrapment efficiencies. Moreover, this method, based on acetonitrile-induced colloidal dispersion dissolution and centrifugation, could be useful for determination of acetonitrile-soluble substance in nanocarrier systems.