The seismic performance of old R/C medium-rise residential buildings before and after slit installation on short columns is studied and compared by conducting the nonlinear frame analysis considering column strength deterioration. The study has revealed that, 1) when ground motions with the maximum velocity of 75 cm/s are considered, the possibility of collapse for the building with slits is greatly reduced because the deformation capacity of short columns is improved, but 2) when ground motions with maximum velocity of 25 cm/s are considered, the amplitude of inter-story drift for the building with slits increases due to the elongation of initial period and the increase in inter-story drift at maximum strength.