Emerging ubiquitous wireless networks are being spread widely. Ubiquitous wearable computers (UWCs) which may contain various communication protocol modules such as WLAN, Bluetooth, ZigBee, Wibro, and CDMA can be a solution in this era to support the ubiquitous wireless network environment. In ubiquitous wireless environments, ubiquitous wearable computers(UWCs) with multiple communication modules can control each communication module as a coordinator and communicate with other devices containing WLAN and ZigBee modules in the surrounding networks. Since IEEE802.15.4 ZigBee and IEEE802.11b WLAN share the same 2.4GHz ISM band, WLAN causes severe interference to ZigBee devices due to higher transmission power in a large bandwidth of 22MHz. We propose a UWC-aided coexistence algorithm in an overlaid network environment of WLAN and ZigBee networks to solve this problem, and measure the performance of WLAN and ZigBee communication modules for two scenarios in a real network testbed in terms of frame error rate (FER) and goodput.