Use of low concrete strength (in some structures as low as 8-10 MPa), structural irregularities, poor detailing in members are some of the significant parameters causing inadequate seismic resistance of deficient RC buildings. Observations made after many earthquakes show that sufficient amount of structural wall with symmetrical arrangement improves seismic performance of RC building and can eliminate the adverse effect of structural deficiencies. In this study, effect of shear wall ratio on the seismic performance of buildings having inadequate seismic resistance was investigated in order to determine the critical shear wall ratio. Two different buildings which have been heavily damaged or collapsed in August 17, 1999 Kocaeli Earthquake, Turkey were selected. Although the plan views, member dimensions, section dimensions and the reinforcement details are available, there is no information about material properties that were used in buildings. Despite this, considering the Turkish building stocks, concrete compressive strength and yield strength of reinforcement bar can be estimated as 10 MPa and 220 Mpa, respectively. Then, building models with shear wall ratio of 2, 1.5, 1, and 0.5 percent and models of existing plans were generated in SAP2000 and nonlinear response history analyses of models were performed. The strong ground motion was selected from Düzce station, which has the highest peak ground acceleration during Kocaeli Earthquake. Variation of roof displacement and inter-story drift ratios with different shear wall ratios were obtained and results were compared. Analysis results of two different buildings showed that building without shear walls responded worse under the selected strong ground motion and that was confirmed by the seismic behavior of structure in 1999 Kocaeli Earthquake. But, when the structural wall ratio increases, seismic performance of the buildings improves considerably.