In this paper, design of a cosecant squared beam collinear dipole array using genetic algorithm (GA) is presented. Cosecant squared beam provide flat power density and it have been mainly used for a radar and base station. The array antenna design using GA is not to require the calculation of derivatives and easy to deal in various variables. In this presentation, the cosecant squared beam collinear dipole array is designed using GA by controlling only a phase and element spacing in order to eliminate the loss of attenuator to control the amplitude. As the result, the smooth cosecant squared beam is obtained from 10° to 42°.