The aim of this paper is to examine the shear resistance mechanism of seismic retrofitting by external reinforcement，which consist of divided thin steel plates and continuous fiber sheets with grout mortar layer，for existing RC short columns．This paper mainly describes the shear effectiveness by the ribs of steel plates in a short columns．In order to investigate the above objects，lateral loading tests were conducted for the six specimens with two types of fiber sheets，with different of ribs width and the steel materials．The test results show that this method is very effective in enhancing the shear strength by ribs of providing steel plates，and a shear resistance which consists of elements of a lateral ribs and fiber sheet was supposed．Based on these results，the study indicates that the shear capacity can be estimated using the design guideline for ultimate shear strength issued by AIJ in 1990.
