This article presents a detailed study on the effect of isolator parameters on the seismic responses of base-isolated (BI) building frames. For this purpose, a five-story base-isolated building frame equipped with lead core rubber bearing (LCRB) as the base-isolation system was considered. The main objective of this study is to investigate the influence of various key LCRB parameters on the responses of BI buildings under near-field (NF) and far-field (FF) seismic ground motions. The parameters selected for this study are isolation time period, damping ratio, and normalized yield strength, whereas the critical responses selected for this study were bearing (isolator) displacement, roof acceleration, and base shear. The results indicated that the parameters’ influence on the responses is similar for near-field and far-field earthquake ground motions. However, BI buildings are more vulnerable to near-field earthquakes. Results also show that to get maximum control of base shear and roof acceleration, a lower normalized yield strength value should be chosen, whereas to achieve lower bearing displacement, a higher normalized yield strength is ideal. The bearing displacement increases with an increase in the flexibility (i.e., increase in isolation time period) in BI building, although roof acceleration and base shear reduce. Up to a certain damping ratio is recommended to achieve optimal seismic control in base-isolated buildings.