Nowadays, communication systems are faced by unprecedented increase in demand of capacity and quality.Population growth and therefore number of users' growth and intensification in electromagnetic waves radiation altogether, have created the need of using advanced communication systems which utilise the available resourses like bandwidth or transmit poweras much as possible. This requirment upholds MIMO systems as the main options for the next generation of wireless systems. In one of the latest approaches in MIMO systems, employing massive number of antennas is considered. By this implementation, communication systems in addition of benefits which they achive from adding more antennas, in asymptotic case they can gain even more. On the other hand, increasing number of antennas causes more power consumption in the system. Due to the worries about global warming and radiated electromagnetic power, Energy-Efficiency study in these systems becomes very important. This raises the question if all of antennas contribute equally to the performance of the system? It is shown by this thesis that using appropriate number of antennas according to number of users and/or required data rate in each transmit and receive interval will cause more effective power usage in the system and consequentlyimprovethe Energy-Efficiency. Also, by noting that there aremassive number of available antennas in the system, it is possible to give priority of usage to those antennas which have better channel condition rather than others. This will cause furtherimprovement in Energy-Efficiency. In this thesis an antenna selection algorithm in base station of cellular massive MIMO systems is proposed. In order to present a realistic model, Energy-Efficiency parameter is defined considering power consumption ofall system's parts. Also, mathematical analysis of the proposed algorithm is expressed to achieve important deterministic results. Eventually, performances of proposed algorithm and a near optimal antenna selection algorithm designed for traditional MIMO systems, using massive MIMO settings are compared. Simulation results reveal the advantage of proposed algorithm. Keywords : Massive MIMO, Energy-Efficiency, Antenna selection, Wishart theorem, 5G wireless cellular communication systems