Practical ships have different operating speed, draft and trim for every load conditions. Therefore, in the case of hull form improvement, it is necessary to develop a different hull form for every condition, from a viewpoint of hydrodynamics. The present paper proposes a hull optimization method for reducing wave-making resistance using the real-coded genetic algorithms in multiple load conditions. The real-coded genetic algorithm of the optimization method, employs UNDX (Unimodal Normal Distribution Crossover) as a crossover operator, and employs POSS (Pareto Optimal Selection Strategy) as a generation-alternation model. The hull optimization for Series60 (CB=0.6) is carried out using the program which is based on the present method. In the optimization, many Preto solutions are obtained. These hull forms have low wave-making resistance by the panel-shift type Rankine source method on the full load condition and ballast condition comparing with the original hull form.