Abstract: Accurate estimate of available bandwidth can make the Ad hoc network resources be used reasonably and effectively. A novel available bandwidth estimation mechanism based on frame retransmission prediction is proposed. The average size of contention window (CW) is used to evaluate the collision status and the number of frames that need to be retransmitted, and the estimation procedure is accomplished with the method of cooperation between mobile nodes. Results show that the method based on the average size of contention window can evaluate the frames collision status on the link with reasonable accuracy.