In today's world, the use of cloud data centers for easy access to data and processing resources is expanding rapidly. Rapid technology growth and increasing number of users make hardware and software architectures upgrade a constant need. The necessary infrastructure to implement this architecture is the use of virtual machines in physical systems. The main issue in this architecture is how to allocate virtual machines to physical machines on the network. In this paper we have proposed a method to use virtualization for minimizing energy consumption and decreasing the cloud resource waste. We have used learning automata as a reinforcement learning model for optimal placement of virtual machines. The simulation results show the proposed method has good performance in reducing energy consumption of servers in cloud data centers.