While olive oil is an important food product in the Mediterranean Sea Basin, olive oil mill wastewater (OOMW) and olive pomace, which are by-products of olive oil, are released in excessive quantities. OMWW is an important source of environmental pollutants due to its slightly acidic pH, high contents of phenol and chemical oxygen demand (COD). To overcome this problem, it was aimed to investigate the potential use of OOMW as an alternative substrate for biomass production by filamentous fungi in this study. For the cultivation, three edible fungi (Aspergillus oryzae CBS 819.72, Neurospora intermedia CBS 131.92, and Rhizopus delemar CBS 145940) were tested. Among them, A. oryzae was found to be a promising fungus in biomass production containing 14.9% protein. The protein content of the biomass was improved to 44.9% (w/w) by adding a nitrogen source (sodium nitrate) and removing the suspended solids. Concomitantly, 35-44% of COD reduction was also obtained after the fungal cultivation. Thus, the potential use of olive oil mill wastewater for the cultivation of fungal biomass was determined and at the same time, its pre-treatment was provided. However, the content of the obtained fungal biomass should be determined and its usability as feed should be investigated.