This paper introduces a new application of genetic algorithm (GA) in dynamic sector synthesis of antenna array for mobile base transceiver station (BTS). The basic objective is to have narrow beam widths in heavy handoff areas and wider beam widths in areas with low traffic density. By predefining the beam widths and thus the beams of each sector, optimal sectoring can be achieved using GA at different time of the day as traffic changes. The proposed algorithm consists of the simple GA with new adaptive mutation mechanism. When compared with simple GA, the proposed algorithm shows faster convergence. The results obtained are more stable and having higher fitness.