A progressive collapse resistance experiment was made of a two storey steel frame. The composite concrete slab was adopted and the action of the concrete slab was considered according to the theory of the composite beam during the design process. In order to simulate the instantaneous failure of the column, the horizontal force was implemented suddenly to the top of the column through a hoisting machine. Experimental results show that the test frame has enough redundancy because of the streghtening of the composite slabs. The composite beams have the higher flexure stiffiness because the composite slabs and steel beams work together through the shear studs on the top flanges. The columns and beams of the remainder structure do not fail further after the instaneous column removal due to the formation of the alternative load path. It is indicated that the steel frame with composite slabs has the higher redundancy and horizontal tie forces according to the present design method. The action of concrete slabs needs a reevaluation in the analysis of progressive collapse resistance.