We studied the capacity of extreme halophyte, Arthrocnemum macrostachyum, to desalinize an experimentally-salinized soil under non-leaching conditions. Furthermore, we tested the effect of salt pre-exposure of this species on its phytodesalination capacity. The presence of the halophyte, independently salt pre-exposure, decreased salinity of the sanilized soil by 31% after 30 days; reducing the negative effects on emergence of both test cultures, barley and wheat. Plants of A. macrostachyum pre-treated without salt showed 4-fold higher relative desalination rate than those grown with optimum salinity (with higher initial biomass). Thus, previous salt exposure was as determinant as plant biomass for desalinizing capacity. In conclusion, pre-exposure to salt of halophytes must be taken into account for desalination programs.