It is necessary to estimate damage levels of RC columns precisely in large plastic deformation range for reasonable seismic resistant design. We carried out reversal cyclic loading tests by RC model columns with large deformation capacities, and estimated damage levels correspond to plastic deformation levels in consideration for easiness of repairs. Furthermore, ranges of serious damages were examined. We also carried out reversal cyclic loading tests by repaired RC model columns, and repairing effects were confirmed. From these experiments and examinations, damage levels for seismic resistant design and repairing effects of RC columns in large plastic deformation range were made clear.