Abstract: The properties of ultrashort pulse propagation in metamaterials (MMs) are investigated, and special attention is paid to the anomalous phenomena of pulse splitting inaccessible in ordinary materials. It is found that the interaction of anomalous group velocity dispersion(GVD) and self-defocus effect will lead to the symmetric pulse splitting due to negative index in MMs. In addition, we have investigated the influence of controllable self-steepening(SS) induced by dispersive magnetic permeability on the pulse splitting. It is shown that both positive and negative SS lead to the asymmetric pulse splitting in MMs. Analysis shows that negative SS effect gives rise to the trailing pulse being higher than the leading pulse, same as the corresponding case in ordinary material;positive SS in MMs causes the opposite of the previous case, namely, the trailing pulse being lower than the leading pulse.