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An important advantage of cold-formed steel is the great flexibility of cross-sectional profiles and sizes available to structural steel designers. However, this flexibility makes the selection of the most economical section difficult for a particular situation. In this study, Micro Genetic Algorithm(μ-GA) is used to find an optimum cross section of cold-formed lipped channel beams under uniformly distributed load considering all structural constraints such as moments, deflection, shear, web crippling, and flange curling. The efficiency of μ-GA has been proved through many problems, especially the problem with 3~5 design variables. The design curves are generated for optimum values of the thickness, the flange flat-width-to-thickness ratio and lip flat-width-to-thickness ratio for unbraced beams. The optimum design curves presented in this paper can be a valuable guide to structural engineers.