Most of the existing back off algorithms adjust the Contention Window (CW) only after the occurrences of collision in wireless networks. To prevent/ reduce further collisions, this paper proposes a sliding CW approach, to be done, after each successful transmission. Based on the current channel status measured by channel utilization and contention ratio, sliding factors are determined to adjust both lower and upper bounds of CW. The NS2 simulation results show that the proposed algorithm significantly outperforms the conventional Binary Exponential Back off (BEB) and Double Increment Double Decrement (DIDD) algorithms in terms of throughput, delay and packet loss.