The adsorption of zinc cations under behenic acid Langmuir monolayers was investigated by means of isotherm measurements, grazing incidence X-ray diffraction and Brewster angle microscopy. The structure of the films was characterized as a function of Zn2+ concentration, for three different counterions (chloride, iodide, bromide) and at two subphase pHs (5.5 and 7.5). At pH 5.5 and in the studied concentration range, Zn2+ adsorption leads to a condensation of the fatty acid monolayer with the same phase transitions as over pure water. In contrast, at higher pH the organic X-phase is evidenced immediately above a concentration threshold without any ion organization. Even though Cu2+ and Zn(2+)cations induce both the fatty acid X-phase, the kinetics of its formation appears strongly different. Indeed, as for Mg2+ and Cd2+, the intermediate new I-structure is evidenced in the course of Zn2+ adsorption although superstructures are observed only for Mg2+ and Cd2+. However, for Zn2+, the I-phase evolves to the final state through a new structure called X' and a continuous X'-X transition. Finally, any effect of the counterion is evidenced neither during the kinetic process nor in the final state.