An apparatus and method for transmitting data by using Multi-round Contention Avoidance (MrCA) are provided. The method includes initializing a contention window for each of a plurality of contention rounds and setting a backoff counter corresponding to a size of the contention window for each contention round, starting from a first contention round to a last contention round, decrementing a backoff counter of a corresponding contention round in a time slot unit and transmitting data when the decremented backoff counter is zero and when the corresponding contention round is a last contention round. Accordingly, the number of contending nodes is exponentially decreased for each contention round, resulting in significant decrease in a collision probability in addition to improving fairness on channel use among users.