In order to develop an effective seismic shear strengthening method for improving the earthquake behavior of existing R/C short columns, experimental studies are conducted by using four beam-column sub assemblage specimens with a short column. Three short columns of these specimens are strengthening by steel plates and concrete, while other one is without any steel plate strengthening. All the specimens are tested under a constant gravity load and alternately repeated lateral forces. Test results demonstrate that, if the short column is strengthened by a welded square tube and concrete, then brittle shear failure does not occur and the column can develop its ultimate flexural moment capacity. It is also shown by tests that the proposed strengthening method using steel plates and concrete is applicable to repair and rehabilitate the damaged short columns failed in the brittle shear mode.