The purpose of graduation thesis was to learn more about the factors that influence the quality of olive fruit and how it affects the quality of olive oil. Olive tree is a typical Mediterranean plant. But if we want to produce quality fruits, we must carefully plan the orchard design and planting of the orchard, later properly cultivate the soil, fertilize it, perform a regular pruning and take care of the appropriate plant protection against diseases and pests. For the best quality of oil, it is also important to take care of the harvesting and processing of the fruit, as mistakes can quickly occur. It is crucial that the fruit remain undamaged after harvest and that they are processed as soon as possible. The parameters that are measured and monitored for determining the quality of olive oil are: free fatty acid content, peroxide value, total phenol content, oxidative stability, UV absorption at 232 and 270 nm, antioxidant activity and fatty acid composition. For the highest quality of oils - extra virgin olive oils, sensory evaluation is also necessary for quality assessment. In olive oil, the highest oleic acid and antioxidant content (especially α-tocopherol) is desired and the presence of free fatty acids should be as low as possible. The processing of non-quality fruit has negative effects on the flavours of olive oil, and there are off taste such as: wormy, moldy, overheated, acidified, brine, hay/wood and moist wood.