The effectiveness of prefabricated composite jacketing to retrofit existing circular reinforced concrete (RC) bridge columns for enhanced seismic shear strength is described in this paper. The jackets consist of multilayer prefabricated glass fiber reinforced composite shells adhered together. Three half-scale circular columns were tested under cyclic shear in double curvature and constant axial load. One column was tested in the "as built" condition to investigate the shear failure mode of columns designed based on pre-1971 codes. Two other columns were tested after being retrofitted using prefabricated composite jackets. The as built column suffered shear failure at low displacement ductility. The retrofitted columns developed significantly improved hysteretic responses with stable hysteresis loops even at displacement ductility levels as high as 10.0 corresponding to drift ratios exceeding 5.2%. Method for retrofit design using prefabricated composite jacketing is also provided and validated by the test results.