Two olive mill pomace samples from two Split-Dalmatia county’s olive mills with different types of production were characterized. Water content for 3-phased process sample is determined to be 51.2% and 67.9% for 2-phased process sample. Organic matter content has been determined to be 97.95% for the first sample and 95.47% for the second one. By leaching the 3-phased process olive pomace sample with distilled water, three samples of olive pomace leachate were obtained, one for each day of leaching. COD and BOD 5 values of three leachate samples were determined, as well as pH value, turbidity and Kjeldahl nitrogen content. After the first day of leaching, the sample showed the highest organic matter content with extremely high COD value of 4736.2 mg O 2 /L and BOD 5 value of 2650.0 mg O 2 /L, along with turbidity of 188.0 NTU, pH value of 4.97 and Kjeldahl nitrogen content of 22.4 mg N/L. Considering the given parameters, wastewater must not be released in natural waters nor the sewage system, according to the Croatian Policy of limiting values of wastewater emissions. Second and third day of leaching produced wastewater samples with significantly lower parameters which confirm leaching of the olive pomace as a harmful process in case of exposing of the pomace on unprotected open area.