In this paper, a beam-tracking technique for orthogonal frequency division multiplexing (OFDM)-based millimeter-wave cellular systems is proposed using subarray structures and pilot sequences. In order to track the variations in the angle of departure (AoD) and angle of arrival (AoA), an antenna array is configured into two different subarrays, which allow us to estimate AoD/AoA based on the phase difference between the two subarrays in the received signals. A pilot sequence is designed such that it can distinguish between different subarrays and track a beam for a mobile station in multicell multiuser environments. Two different implementation methods of AoD/AoA estimation are proposed and compared with computer simulations.