This paper presents a Pareto Based Optimization Algorithm to determine the best part orientation in Stereolithography systems. The previous methods could either handle simple parts or limited Objective Functions (OF). Moreover the methods with multiple OFs, had abstracted them into a single fitness function. A single fitness function never reflects the characteristics of individual OFs properly. The method proposed here handles several OFs individually. The objective functions are minimum build time and minimum support volume under desired surface finish. The optimization is done using Genetic Algorithm (GA). At each GA step, the surface finish is achieved applying adaptive layer thickness method. Pareto Based Optimization (PBO) finds the best part orientation with minimum build time and volume support. PBO is a multi objective optimization to handle complex CAD files. The algorithm is developed by MATLAB. The codes are run for some case studies. The results are very promising.