This study aimed to obtain an extract rich in polyphenols from olive stones using a pilot scale pressurized water extractor, and microencapsulate this extract using a spray dryer. The optimization study focused on the evaluation of the stabilization of the polyphenols and antioxidant effects of the microcapsules obtained. The polyphenol extract of the olive stones obtained under optimum extraction conditions (50 degrees C, 50 bar, 90 min) was microencapsulated by using 1% chitosan solution as the microencapsulation agent. The total polyphenol contents (TPCs), total flavonoid contents (TFCs), individual polyphenol contents and antioxidant capacities (DPPH and FRAP) of the polyphenol extract and the microcapsules, which were obtained using 200 degrees C as the optimum air inlet temperature in the spray dryer, were determined. For the evaluation of stability, these microcapsules were stored at three different temperatures, namely - 20 degrees C, 4 degrees C and 25 degrees C, for 180 days. Changes in their TPCs, surface polyphenol contents (SPCs), microencapsulation efficiencies, TFCs and antioxidant capacities were determined every 30 days and their individual polyphenol contents were characterized at both the beginning and the end of the storage period. The encapsulation efficiency of the microcapsules obtained under optimum conditions was 76.89%. At the end of the storage period, the highest degradation of the related compounds was found at - 20 degrees C. Moreover, it was found that the polyphenols (24.17% for TPC, 53.73% for SPC, and 39.31% for TFC) and antioxidant capacities (15.63% for antiradical effect, and 20.39% for FRAP) of the microcapsules were best preserved in storage at 4 degrees C. It was thought that aforementioned condition was suitable for the storage of microcapsules which could be evaluated as a new natural food additive or pharmaceutical ingredient.