It is predicted that there will be billions of machine type communication (MTC) devices to be deployed in near future.This will certainly cause severe access congestion and system overload which is one of the major challenges for the proper operation of 5G networks.Adopting device-to-device (D2D) communications into massive multiple-input multiple-output (MIMO) systems has been considered as a potential solution to alleviate the overload of MTC devices by offioading the MTC traffic onto D2D links.This work proposes a novel pilot reuse (PR) and power control (PC) for energy efficiency (EE) optimization of the uplink D2D underlaying massive MIMO cellular systems.Although the use of large scale antenna array at the base station (BS) can eliminate most of the D2D-to-Cellular interference,the Cellular-to-D2D interference and the channel estimation error caused by PR will remain significant.Motivated by this,and in order to reduce the channel estimation error,in this paper a novel heuristic PR optimum pilot reuse scheme is proposed for D2D transmitters (D2DTs)selection.By taking into account the interference among users as well as the overall power consumption,the overall system EE is maximized through power optimization while maintaining the quality-of-service (QoS)provisions for both cellular users (CUEs) and D2D pairs.The power optimization problem is modeled as a non-cooperative game and,as such,a distributed iterative power control algorithm which optimizes users’ power sequentially is proposed.Various performance evaluation results obtained by means of computer simulations have shown that the proposed PR scheme and PC algorithm can significantly increase the overall system EE.