In this study, it was aimed to find the optimum condition for extraction of phenolic compounds from olive pomace by using high-pressure-assisted extraction (HPAE). In this method, different pressure parameters (300-500 MPa), times (5-15 min), and ethanol concentrations (50-90% v/v) were used. According to Box-Behnken design, 15 experimental runs were performed to find the optimum condition of total phenolic and oleuropein contents. Also, the optimum HPAE condition was compared with that of classical solvent extraction (CSE). Based on the results, the optimum HPAE condition was chosen as 409 MPa for 11.16 min with 63.74% v/v ethanol concentration. According to ANOVA results, pressure, time, and ethanol concentration had significant effects on the total phenolic content and oleuropein content (p <= 0.05). Compared to CSE, it was found that HPAE increased the total phenolic content, antioxidant capacity, and oleuropein content significantly. According to scanning electron microscopy and Fourier transform infrared spectroscopy results, it was found that the mass-transfer rate of phenolic compounds increased because of morphological changes, but there were no chemical changes in phenolic compounds observed when HPAE treatment was applied. Overall, it can be said that HPAE treatment was an effective method to improve the recovery of phenolic compounds from olive pomace compared to the traditional treatment.