14 global positioning system(GPS) receivers were employed to monitor the deformations of the Nanpu Bridge in Shanghai for 4 consecutive days in September 2006.A dedicated bridge coordinate system was established to analyze and relevant algorithm was used for the coordinate transformation.The precision of the resulting coordinate time series and the static and dynamic characteristics of the bridge deformation were analyzed.Analysis results show that GPS positioning is fully capable to monitor the deformations of medium to large size bridges and the critical parameters about the structural health conditions of these bridges can be reliably extracted from the 3D coordinate time series.Through the trial,it further proves that GPS positioning technique has unique merits over other traditional monitoring tools.