In performance-based engineering, conservatism in acceptance criteria at structural performance levels has increased the cost of retro tting. In seismic rehabilitation of structures, uncertainties associated with existing structures have been studied and rehabilitation guidelines have been applied to deal with these uncertainties in terms of reliability index. The secondary system, which is added to the existing structure, is subject to uncertainties in seismic rehabilitation of structures. These uncertainties can escalate the uncertainties of rehabilitated structures and may change the analysis results such as reliability index parameter, values of fragility, and inter-story drift. Therefore, this study investigated the reliability of the structure rehabilitated with steel shear wall and performed a parametric study on the reliability index. The selected structure was a steel moment frame, which was rehabilitated by the steel shear wall. The structure was subject to incremental dynamic analysis before and after rehabilitation with probabilistic variables. Based on the results, the values of the reliability index were obtained for the rehabilitated structure in the presence of uncertainties. According to results, structural rehabilitation reduced failure probability and consideration of uncertainties in the rehabilitated structure increased the probability of failure. Therefore, existing conservatism was reduced.