Stereolithography has the most portions through rapid prototyping techniques in injection molding and vacuum casting manufacturing because of simultaneously possessing of dimensional accuracy and strength. However low surface finish and appearance of stair-step phenomenon, restrict extension of use of this process. In this research, the influence of process parameters and part orientation on surface finish was studied. For this purpose parts were built in various conditions of surface angle, hatch space and post curing time. Surface roughness measured by contact and non-contact method. Surface angle was in 0-180 degree range by 2 degree step. Considered post curing time was 20, 50 and 80 minute and hatch spacing was 50, 75, 100 and 125 micrometer. In non-contact method using digital microscope, surface profile obtained and then surface roughness calculated using MATLAB software. Finally using Analysis of Variance (ANOVA) a mathematical model has been developed among parameters and responses. Results showed that surface finish has reverse relation with hatch space and are almost Independent of post curing time. Surface roughness in up-facing increases with surface angle enhancement swiftly and then it drops. In down-facing Surface roughness increases with surface angle enhancement slowly and then it falls. Comparison of real dates with estimated values showed that estimation average error is less than 14 percent.