In the contention access period (CAP) of IEEE 802.15.4 beacon-enabled mode, collision probability increases, and network performance decreases as the number of contending devices increases. In this paper, we propose an enhanced contention access mechanism (ECAM) to reduce the collision probability in low rate — wireless personal area networks (LR-WPANs). In ECAM, since the duration of each CAP is divided into multiple sub-CAPs, the number of devices contending for frame transmissions in each sub-CAP can be reduced by approximately one over the number of sub-CAPs. Further, this lowers the probability of collision due to two or more simultaneous frame transmissions. In addition, since ECAM shortens the channel access duration of devices, devices with ECAM have lower power consumption. To compare the performance of ECAM with that of the IEEE 802.15.4 standard, we carry out extensive simulations. The results show that ECAM yields better performance than the IEEE 802.15.4 standard, especially for dense networks with a heavy traffic load.