The maximum independent set problem is a classic graph optimization problem. It is well known that it is an NP-Complete problem. In this paper, an improved simulated annealing algorithm is presented for the maximum independent set problem. In this algorithm, an acceptance function is defined for every vertex. This can help the algorithm find a near optimal solution to a problem. Simulations are performed on benchmark graphs and random graphs. The simulation results show that the proposed algorithm provides a high probability of finding optimal solutions.