This paper presents how to optimally minimize the relative sidelobe levels of linear and planar arrays by simple method. Genetic algorithm (GA) is used to optimize the arrays, by thinning and changing the relative spacing of the arrays at the same time. In this technique, the gene of each element has two parts one for the spacing and the other for excitation. Also, Simulation results for linear and planar arrays are depicted. GA is used to determine which elements are turned off in a periodic array to yield the lowest relative sidelobe level (rsll), and also to determine the optimum spacing between the elements.