In this paper, the optimization of the system energy efficiency (EE) is studied for a reconfigurable intelligent surface (RIS) assisted full-deplex (FD) communication system. In the studied model, two devices communicate with each other using one RIS under the FD mode. Each of the devices will receive not only the message from the other device but also the self-interference. The main problem of this work is to maximize EE by jointly optimizing the reflection coefficients matrix and the transmit power of devices. To solve this problem, a nonlinear fractional programming based algorithm is used to transform the fractional optimization problem into a subtractive problem. Then the transmit power and the RIS phase shifts matrix are optimized by an iterative method. Simulation results show that the proposed scheme can achieve up to 200% gain in terms of EE compared to a conventional RIS assisted half-duplex mode.