Abstract.The seismic properties, failure characteristics and lateral load-deformation curves of the three specimens were investigated by testing two specimens retrofitted with CFRP(carbon fiber reinforced polymer)sheets(fabrics) and one specimen without any attachments and by attaching CFRP sheets to the two specimens in two ways. At the same time , the strain level in CFRP sheets on one of specimens was investigated. It came to the conclusion that CFRP sheets were able to improve the seismic properties of concrete hollow block structures significantly and the patterns in which CFRP sheets were attached to structures were a dominating factor influencing retrofit effects. The equations for the shear carrying capacity were presented by introducing a truss model. The validation of the equations was made by contrast of computed values and observed ones and it can be used as a reference to design retrofitted structures.