This paper investigates the effect of operating fogging cooling system on gas turbine on its performance, technical and economic study. This study was made for both 4 hours and 10 hours of operating fogger by actual data from power plant in Egypt. The technical study shows that the maximum increase in power is from 18 to 20 MW. When the ambient temperature increased from 25 to 40 C during a typical summer day, The power jumped from 220 to 238 MW after the operation of fogger. Moreover, The specific fuel consumption decreased from 0.218 to 0.214 (1.8% reduction) and the electric efficiency changed from a minimum value of 35% to 35.8 %. The economic indicators such as the net present value (NPV), Internal return rate (IRR), rate of return (ROR), and pay pack period were obtained. The economic study recommends the operation of fogger from 10 AM to 8 PM. The study showed that there is no economic justification when operating the fogger 4 hours because the net present value (NPV) is – 902,716 $ for discount rate of 10% during the period of 20 year. But when operating the fogger 10 hrs. Daily in summer, the net positive value (NPV) is 4,522,493 $, Payback period=5 years, and the internal return rate (IRR) is 26 %.