Occurrences of olive mill wastewater (OMW) amendment on several chemical and biochemical properties of soil were investigated. Compared to the control, soils amended with untreated and treated OMW (by an integrated process based on aerobic fungal pre-treat-ment using Phanerochaete chrysosporium DSMZ 6909 followed by anaerobic treatment) showed high levels of organic and mineral mat-ters. Soil amended with untreated OMW presented low levels of total and inorganic nitrogen (0.38 and 0.08 mg g~(-1) dry soil). Treated OMW contained little content of pollutants (COD=4 gl~(-1); phenolic compounds=0.6 gl~(-1)); so, organic matter brought by these res-idues was rapidly mineralized in the soil. The number of heterotrophic bacteria was increased (from 54×10~5 CFU g~(-1) dry soil in control soil to 123×10~5 CFU g~(-1) dry soil) in response to the OMW amendment, mainly after C/N ratio correction. Untreated OMW applica-tion improved the soil carbon content (2.18 times higher), while the specific respiration remained very low. However, the treated OMW application positively affected the soil-specific respiration that increased from 6.1 in control soil to 9.75 in soil amended with treated OMW. This phenomenon was accompanied by an enhancement of nitrifiers number, urease and ammonium oxidases activities.