An in situ pushover test is carried out on an old building of Guan-Miao elementary school in south Taiwan. Columns of this building are seismically retrofitted with steel plate. The DIC (digital-image-correlation) technique is used to measure the deformation of the retrofitted column. The result shows that the DIC technique can be successfully applied to measure the relative displacement of the column. Additionally, thismethod leads to the measurement of relative displacements formany points on the column simultaneously. Hence, the column deformation curve, rotation and curvature can be determined using interpolation method. The resulting curvaturediagram reveals that the phenomenon of plastic hinge occurs at about 2% storey drift ratio, and that the DIC technique can be applied to measure column deformation in a full scale in situ test.