This paper introduces an improved steel jacketing method to retrofit reinforced concrete columns with a square or rectangular section for enhanced strength and improved ductility. To retrofit an existing column, relatively thin steel plates were welded to form a rectilinear jacket for shear strength enhancement, and then additional confinement elements stiffeners! with various types of desired configurations were welded to the potential plastic hinge regions to ensure a ductile behavior. A rational retrofit design procedure was suggested and evaluated through an experimental program. Five 1/3 scale model columns were tested under constant axial load of 0.3Ag f c8 and cyclic lateral force in a double-curvature condition. Test results validated the efficiency of the partially stiffened rectilinear steel jacketing, which not only prevented brittle shear failure but also greatly improved the ductility of the column with achieving an ultimate drift ratio of more than 8%. Besides the structural merits, the partially stiffened rectilinear steel jackets also have appealing architectural features.