The determination of total phenolic compounds of olive fruits harvested in three phases of fruit maturity (green, semi-matured and matured fruit) was done at the Institute for Adriatic Crops and Karst Reclamation. According to the planned project activities 27 samples of olive fruits of the cultivars Lastovka, Leccino and Frantoio were analyzed on the High-performance liquid chromatography (HPLC) device.