The biologically active agents may be defined as a natural unnutritious physiological active ingredients which have specific functional properties in the organism.They act as adjuvants in preventing and treating diseases, thus improving the state of the organism. The total antioxidant capacity of food shows how antioxidants (previously analyzed biologically active agents such as phenol) can destroy free radicals in certain food. The aim of this study was to determine the bioactive substances of antioxidant capacity of the plant infusions in three different varieties of the Istrian olive. This study used leaves of Istrian olive varieties: Rosinjola, Buža and Istarska Bjelica. Leaves were harvested in July 2015 in the area of Agricultural Institute Poreč.All measurements were performed in the laboratory.Using colorimetric and spectrophotometric methods for determination of total phenols, flavonoids and nonflavonoid phenols and total antioxidant capacity (ABTS and FRAP methods) is followed by the impact of graduation on leaves (finely ground, rough ground and whole) and the effect of time (5 minutes, 15 minutes and 30 minutes) on the result of extraction.All laboratory measurements were performed at the Center for Materials Research in the Istrian County. The results of the measurements are expressed as average values of three measurements with the corresponding standard deviations. The obtained results show that the gradation of a leaf has a major impact on the antioxidant capacity of infusionwith finely ground leaves showing the greatest amount of extracted substances.Similarly, the extraction time is also very important because the highest concentration ofphenols was achieved in a time of 30 minutes. It was also confirmed that the total phenols and total nonflavonoids have a major impact on the antioxidant capacity of all three varieties of olives.Of the three varieties of olives I would recommend Rosinjola because on the basis of our results it showed the highest concentrations of phenols, flavonoids and nonflavonoids.