In the current study, nonlinear finite element approach was utilized to investigate the behavior and collapse mechanism of RC multistory frames subjected to earthquake motion. Since it is not an economic procedure to design structures to respond to earthquake loads in their elastic range, dissipation of energy by post-elastic deformation has been recommended in the last decades. Plastic hinges are specific zones at structural members where energy is dissipated through the plastic deformation without significant failure of the whole structure. This idea is an extension of the ductile design concept in building seismically resistant enoughductile and limited-ductile reinforced concrete frames. So the nonlinear behavior of multi-storey RC frames under earthquake loading and the corresponding failure mechanisms were studied. The plastic hinge is assumed to occur when steel reaches yielding or concrete reaches ultimate strength. In all cases, yielding of steel occurs first because the sections are designed to be under-reinforced sections. The behavior of RC multistory frames is investigated focusing on propagation of plastic hinge as affected by number of stories, grade of concrete and changing of main reinforcement ratios under the effect of three input motions. The nonlinear behavior is represented by the following items: angle of beam and column rotation; time of first beam and column hinge occurrence; total number of beam and column hinges; maximum induced base shear; peak relative horizontal acceleration; peak relative horizontal displacement; and Interstorey drift diagrams. Several conclusions are drawn out for future design of RC multistory frames.