In this paper the progressive collapse resisting capacity of steel moment frames with MR dampers is evaluated, and a preliminary design procedure for the dampers to prevent progressive collapse is suggested. Parametric studies are carried out using a beam-column subassemblage with varying natural period, yield strength, and damper force. Then the progressive collapse potentials of 15-story steel moment frames installed with MR dampers are evaluated by nonlinear dynamic analysis. The analysis results of the model structures showed that the MR dampers are effective in preventing progressive collapse of framed structures subjected to sudden loss of a first story column. The effectiveness is more noticeable in the structure with larger vertical deflection subjected to larger inelastic deformation. The maximum responses of the structure installed with the MR dampers designed to meet a given target dynamic response factor generally coincided well with the target value on the conservative side.