Micellar and surface properties of hexadecylpyridinium bromide in various water/ 1,2-ethanediol mixtures were determined using membrane electrodes selective to the surfactant ion and surface tension and conductivity measurements at different temperatures. The critical micellar concentrations (CMC) and surface properties, such as surface excess concentrations, minimum area per molecule, and surface pressure at the CMC, as well as the thermodynamic quantities of adsorption and micellization were calculated. The effective dissociation of the micelles (alpha) was evaluated by three different methods. From the dependency of the thermodynamic properties of micellization and adsorption on the concentration of 1,2-ethanediol, it can be concluded that micelles do form in these systems. The aggregation number and the size of the micelles decrease in a 1,2-ethanediol-rich mixture with water.