Wireless Local Area Networking standard (Wi-Fi) and the WPAN standard (Bluetooth and Zigbee) products utilize the same unlicensed 2.4 GHz ISM band. Co-existence between such wireless technologies within the same frequency spectrum is crucial to ensure that each wireless technology maintains and provide its desired performance requirements. In this paper, we investigate the coexistence of WLAN (IEEE 802.11g) with Zigbee (IEEE 802.15.4) standard. The paper focuses on quantifying potential interferences between Zigbee and IEEE 802.11g by examining the impact on the throughput performance of IEEE 802.11g and Zigbee devices when co-existing within a particular environment. In addition, the effect of Zigbee on IEEE 802.11g was compared with the effect of Bluetooth under the same operating conditions.