Seismic profiling together with seismic refraction data and dredging enabled us to study the upper crustal structure of the Tonga-Kermadec trench and the Ozbourn Seamount junction area. Horst-graben structures have been revealed both on the insular and oceanic slopes of the trench. Two systems of faults are characteristic: one transverse and the other parallel to a general trend of the Tonga-Kermadec trench. Grabens of the trench insular slope are partly compensated by sediments unlike those of the oceanic slope which are not ponded by sediments. On both slopes the faults are normal. This testifies to the extensional conditions within the upper crustal part of this region. The Tonga-Kermadec uplift (insular slope of the trench) has undergone intensive (with amplitide to 5–7 km) vertical movements (uplifting and then subsidence) in Eocene, Oligocene, Pliocene and Quaternary times.