This paper expounds the development of a knowledge-based expert system for the optimal strength design of composite structures subjected to various loading conditions and rules of design heuristics. The optimal stacking sequences are obtained by integration of a knowledge-based expert system, genetic algorithm and finite element analysis. Because this expert system in optimal stacking sequence design adopts a finite element method as a stress analysis tool, it isn't limited to laminate design but can be applied to a general composite structure. The optimal stacking sequence combination is drawn from discrete ply angles and rules of design heuristics stored in the knowledge-base for the given application of interest. Results of this study were verified through comparison with quasi-isotropic lay-ups.