Peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS) is a heterogeneous category of nodal and extranodal mature T-cell lymphomas. PTCL-NOS is a highly aggressive lymphoma, and its prognosis is poorer than those of aggressive B-cell lymphoma such as diffuse large B-cell lymphoma(DLBCL). Current standard chemotherapies for aggressive B-cell lymphoma, such as CHOP, are the commonly used regimens for PTCL-NOS, but their efficacies were insufficient and no standard treatment has been established. Role of high dose therapy followed by autologous stem cell transplantation has not been established as an initial treatment. Several new drugs including monoclonal antibodies and molecular target drugs are now under investigation.