This study is intended to discuss changes in modal parameters of a steel truss bridge due to artificial damage through a field experiment. Modal parameters of the bridge are identified by both frequency domain decomposition (FDD) and multivariate autoregressive (AR) model with stabilization diagram. Modal frequencies decreased due to the artificial damage that results in stress redistribution; such a change can be observed when damage was applied at the non-nodal point of the corresponding mode shape. Mode shapes were distorted due to asymmetric damage; mode shapes in the damaged side were deformed clearly as damage was applied at the non-nodal point. Damping ratio was hard yet to use for damage detection.