This paper addresses a multi-period production scheduling problem of an ethylene plant by considering feedstock supplies, plant operating conditions, product inventories and demands simultaneously. The main complexity in solving this problem comes from a mixed integer nonlinear programming (MINLP) formulation of a naphtha feedstock management problem that includes scheduling vessel arrivals, storage tank assignments and blending. In addition, we also consider 4 other feedstocks, nonlinear yield models, separation constraints, product inventories and demands in the model. The number of binary variables in the model for a typical scheduling periods of one month can easily exceed a. thousand. It may well be one of the largest and most rigorous model for ethylene plant production scheduling ever reported to date. Here we will discuss issues related to a problem formulation, solution strategy and industrial implementation of the ethylene plant production scheduling system.