Increasing gasoline and propylene production from Fluid Catalytic Cracking Dnits (FCCDs) has been widely discussed over the past few years. Today, one of the main industrial challenges is how to balance the design and operation of FCCU between maximum gasoline and propylene production. With market demands and prices of both products fluctuating, it is desirable to operate the unit at optimal operating settings to achieve optimum yields. This paper proposes a new Mixed Integer Nonlinear programming problem (MINLP) formulation that aims to minimize the total cost of gasoline and propylene production by obtaining optimal operating settings that generate both products optimal yields as per their respective economic value. A case study is developed to verify the formulation effectiveness. The problem is solved using Matlab genetic algorithm toolbox. The results reveal that the model reacts correctly to prices and demands market fluctuations under various situations.