Progressive collapse is the collapse of all or a large part of a structure precipitated by damage or failure of a relatively small part of it. These efforts tended to focus on improving redundancy and alternate load paths, to ensure that loss of any single component would not lead to a general collapse. To avoid of progressive collapse in structures, some criteria have been considered by regulations that after elimination of a member, structure should have ability to bear applied loads and transfer them to other members using substitution paths. In this study, the effect reinforced concrete slab in performance of steel moment resisting frame in progressive collapse was investigated.in this research a part of roof with structural members and connections were modeled and effective parameters of slab to increase structure capacity and crack propagation path due to corner, lateral and middle column elimination, were evaluated. In modelling, the effects of rebar, concrete strength and slab thickness on strength in different cases of column elimination were investigated. Results showed that moment resisting frame with composite slab have more capacity to bear loads due to column elimination in comparison with frame without composite slab. Also, the rate of increasing strength depends on location of column in the plan.