In order to establish a path from source to destination with less routing cost, we propose a directional probabilistic algorithm to broadcast RREQ packets toward the destination. Without any positioning system, the algorithm uses encounter records to predict the direction to destination and sets different forwarding probability for different intermediate nodes. The simulation results show that our algorithm saves 70% routing cost compared to flooding and 20% compared to pure probabilistic algorithm. Furthermore, the new algorithm also shows good performance in other aspects.