Recently, the interest in olive leaves has increased due to its high phenolic content. Olive leaves have a high potential for industrial exploitation in the food industry and drying is the main process in olive leaf treatment. In this Study, response surface methodology was used to optimize operating conditions of the drying of olive leaves in a tray drier and desirability function used as the methodology for the optimization. Optimization factors were air temperature (40-60 degrees C), air velocity (0.5-1.5 m/s) and process time (240-480 min) while investigated responses were total phenolic content (PC) and antioxidant activity loss (AC), final moisture content (MC), and exergetic efficiency (eta). The optimum conditions for drying of olive leaves in a tray drier were determined to obtain the criteria; minimum PC and AC, and maximum eta for MC value below 6% and the optimum condition was found to be the temperature of 51.16 degrees C with the air velocity of 1.01 m/s for the process time of 298.68 min. At this optimum point, PC, AC, MC and eta were found as 10.25%, 41.88%, 6.0% and 65.50%, respectively. (C) 2008 Elsevier Ltd. All rights reserved.