Abstract: The continuous centrifugation process for olive oil extraction yields three phases: oliveoil, pulp, and olive mill wastewater (OMWW). The latter generates an environmentalcontamination problem. The often demonstrated phytotoxic properties of OMWW could beexploited as a bio-herbicide. In this study, we examined the potential use of OMWW for weedcontrol under sustainable agricultural systems. Net house experiments were conducted using potsfilled with Vertisol soil and sown with three weed species: Silybum marianum, Phalarisbrachystachys and, Daucus carota. Three OMWW application methods were examined: pre-plantincorporated (PPI), pre-emergence (PRE) and post-emergence (POST), applied at four levels: 0(untreated control), 20, 80 and 160m3 ha-1. POST treatments did not significantly injure weedstherefore data of this application method will not be discussed in this paper. PRE treatmentsseverely reduced seedling emergence of dicot species, however, minor reduction in emergencerate was observed in P. brachystachys. PPI treatments moderately reduced weed emergence, yetthey significantly affected weed development. The herbicidal effect of OMWW was also testedunder field conditions. OMWW at rates of 80m3 ha-1 were PRE or PPI (incorporated to 10cmdepth) applied to the soil. Non-treated plots served as a control. Weeds that succeeded to emergein the OMWW treated plots were severely inhibited and appeared chlorotic and thin. In this studywe have shown that OMWW can serve as an efficient bio-herbicide for weed control.