A feasibility study of Bridge Weigh-in-Motion by Reaction Force method using PC-girder bridges was carried out. Strain gauges were attached on edge faces of lower flanges above metal bearings and wireless sensor network were installed at two bridge piers. Calibration and accuracy check were carried out by a test truck with known axle weight. Estimation accuracy was less than 5% for gross vehicle weight and 15% for axle weight. Long term monitoring of 188 hours were carried out and Axle weights of 35,000 vehicles were obtained.