In this study, the effective factors on warpage in short fibre reinforced thermoplastic composites has been studied. First of all, the effective factors in manufacturing process were detected and then in order to decrease the number of experiments, the approach of Design of Experiments has been applied. By using micromechanics theory in composites and coefficients of thermal expansion models, a dedicaded code has been used to set up the experimnts. Then the effect of each significant parameter drived and the most effective parameter on warpage phenomenon is detected. At last by using Taguchi's optimization method, warpage of short fibre reinforced thermoplastic composites has been minimized.