In IEEE 802.15.4 beacon-enabled mode, the personal area network (PAN) coordinator can assign guaranteed time slot (GTS) to allocate a particular duration for requested devices. The main challenge in GTS mechanism is how the PAN coordinator allocates time slot duration for the devices which request GTS. However, if the allocated devices use GTS slot partially or the traffic pattern is not suitable, the wasted bandwidth will increase which make degrade the performance of network. In order to overcome the above mentioned problem, this paper proposes a partitioned GTS allocation scheme (PEGAS) for IEEE 802.15.4 networks. PEGAS aims to decide the precise time for the starting time (GTSstart), the end of GTS (GTSend), and the GTS length (GTSlength) allocation for requested devices taking into the value of superframe order (SO), length of data packet and arrival data packet rate. The simulation results show that the proposed mechanisms outperform the IEEE 802.15.4 standard in terms of total of transmitted packet, throughput, energy efficiency, and latency.