Using directional antennas in wireless ad hoc networks is an attractive issue due to its potential advantages such as spatial reuse, low power consumption and low chance of interference. To acquire these advantages, we propose a new routing scheme called DAPOS (Directional Antenna based Path Optimization Scheme). The proposed scheme enables us to acquire an efficient path by considering the characteristics of directional antennas, resulting a routing performance improvement. DAPOS focuses on shortening the length of routing path gradually by considering the higher gain of directional antennas at a receiver side. Simulation results show that DAPOS significantly reduces the number of hops in route, thereby it improves the overall network performance.