We propose a new backoff scheme, called exclusive backoff scheme (EBS), for ad hoc mode in IEEE 802.11 wireless LANs. Each station generates a unique backoff number before starting backoff procedure by using timing synchronization function (TSF) timer and a unique user's ID (UID), which makes a collision free access. The EBS shows better performance in the view of channel utilization and packet delay than original IEEE 802.11 CSMA/CA backoff scheme.