The Japanese seismic code stipulates a seismic force reduction factor (Ds) to consider the ductility of concentrically braced frames, which varies from 0.25 to 0.5 in accordance with the type of the backup frame, the slenderness ratio (lambda) of braces, and the relative strength carried by braces, namely the participation ratio (beta). In this study, the ductility of braced frames is examined through a model-based analysis, with Ds, lambda, and beta as major variables. It is found that the braced frame has comparable story drifts as the referenced frame regardless of beta, lambda, and the intensity of ground motions, so that it is possible to adopt a unique Ds (or R in UBC97) for braced frames as that for the corresponding pure moment frames.