Pre-dried 2-phase olive pomace was dried until 8% moisture content of it by tray dryer. The effect of tray dryer's process conditions in terms of drying temperature (70-90 degrees C), air velocity (0.5-1.8 m/s), and sample thickness (0.5-1.5) on the quality of olive pomace and system energy efficiency were investigated. Moreover, tray dryer process parameters were optimized considering of minimum drying time, minimum quality loss of olive pomace, and maximum system energy efficiency. The optimum tray dryer conditions were 85.2 degrees C of drying temperature, 1.72 m/s of air velocity, and 0.5 cm of sample thickness as specified by using the Design Expert packaged software. The effects of drying temperature, air velocity, and sample thickness on the physical and chemical properties of dried 2-phase olive pomace (free fatty acid and specific absorption value [K-232, K-270]) and the system's energy efficiency (in terms of the moisture extraction rate and specific energy consumption) were examined.