In this study, an effective numerical procedure for elastoplastic dynamic analysis of three-dimensional steel frames under earthquake loads with three components is presented. The proposed analysis accounts for material, geometric and connection nonlinearities. Material nonlinearity is modeled by the Ramberg-Osgood relation and it is simulated by the formation of plastic zones of zero length at the ends of the elements. Elasto-plastic correction factors are obtained from finite incremental nonlinear member force-deformation relations and then, the member's tangent stiffness matrix is formed by using these factors. Interaction surfaces are described with the lower bound yield surface equations suggested by Morris and Fenves. The geometric nonlinearity has been described by using stability functions and nonlinear behaviour of semi-rigid connections has been taken into account by employing the independent hardening model given by Kishi and Chen. The equation of motion has been solved by Newmark's constant acceleration method in time history domain.