In structural sensing applications, wireless sensing systems have drawn great interest owing to faster installation process and lower system cost compared to the traditional cabled systems. As a new-generation wireless sensing system, Martlet features high-speed data acquisition and extensible layout, which allows easy interfacing with various types of sensors. This paper presents a field test of the Martlet sensing system installed at an in-service pre-stressed concrete highway bridge on SR113 over Dry Creek in Bartow County, Georgia. Four types of sensors are interfaced with Martlet in this test, including accelerometers, strain gages, strain transducers and magnetostrictive displacement sensors. In addition, thermocouples are used to monitor the temperature change of the bridge through the day. The acceleration, strain and displacement response of the bridge due to traffic and ambient excitations are measured. To obtain the modal properties of the bridge, hammer impact tests are also performed. The results from the field test demonstrate the reliability of the Martlet wireless sensing system. In addition, detailed modal properties of the bridge are extracted from the acceleration data collected in the test.