When a manufacturing system is designed, various kinds of evaluation methods are used for selecting the best alternative. Net present value, inner rate of return and payback period are popular quantitative measures for the economic assessment, but other qualitative measures should be considered for evaluation. The analytic hierarchy process(AHP) has been used as the popular method for the multi criteria decision making problem that considers both quantitative and qualitative criteria. This paper explains the process of economic assessment, and how to use the AHP for evaluating the designs of the assembly lines for lens module installed in mobile phone.