Olive mill wastewater (effluents from olive oil extraction during harvest) is a source of environmental pollution due to its high acidity and heavy loads of polyphenols and organics. Our aim is, to study the phytotoxicity of olive mill wastewater (OMW) at different concentrations on the germination and growth of tomatoes (Solanum lycopersicum L). To assess this, we measured the percentage of germination (GP), the germination inhibition rate (GIR), the length of the main stem, the number of leaves, and the biomass of the stem, leaves, and roots. The germination test was carried out by placing 25 tomato seeds on filter paper in Petri dishes and then irrigating with different concentrations of OMW (0%, 1%, 2%, 5%, 7%, 10%). The boxes were placed in an incubator at a temperature of 25 °C for 10 days. The results obtained show that, after 10 days of germination, the GP is maximal (more than 98%) at concentrations of less than 7% (r=-0.98; p<0.000) and with an "inhibitory" effect at more than 7% (r=+0.98;p<0.000). However, the growth in length (8.514±2.612 cm) and the number of leaves (4.667±0.866leaves) were maximum, respectively, at 2% and 1%, after a period of 30 days. However, the dry weight is maximum (0.235±0.049g) at 5% OMW, however, there is no significant difference in the fresh and dry weights of the stems and leaves for different concentrations. In light of these results, the OMW of crushing units using the continuous three-phase process could be used as an irrigation source at concentrations below 7%, for better tomato yield.