Abstract: Routing and Wavelength Assignment (RWA) is a key issue in next-generation optical networks. This paper presents an improved ant colony algorithm (Smart Ant-Dynamic RWA, SA-DRWA) to solve the RWA problem in optical networks. The link idle ratio is introduced into the ant transition probability as new constraint. At the same time, the random disturbance is added to prevent premature convergence into local optimal path within the less iteration. Theoretical analysis shows that the SA-DRWA algorithm can effectively achieve load balancing in optical network. Simulation for different topologies shows that the SA-DRWA algorithm has both improvements of blocking probability and resources utilization comparing with the traditional Dijkstra+FF algorithm. An optimal improvement scenario is obtained in regular mesh network with up to 0.23 improved for blocking probability and resources utilization.