The gravity and magnetic anomalies, seismic and seismological data were analyzed to determine the nature and timing of tectonic deformations in the Laptev Sea and the western part of the East Siberian Sea. Formation of narrow elongated extensional structures (grabens) on the Laptev and East Siberian shelves may be attributed to different stages of evolution. This can occur due to westward shift of spreading activity in the Eurasian Basin which tentatively took place at Oligocene-Eocene interface (chron LMA 13) and in Pliocene. Direct geological observations in the marginal parts of one of the currently passive grabens on the shores of the Blagoveschensky Strait dividing the islands of Novaya Sibir’ and Faddeevsky make possible to determine the time line of deformation cessation in this area. A detailed combine analysis of different data made it possible to derive information on the tectonic events in the Laptev Sea – East Siberia Sea area. The main result is a tectonic subdivision of active deformation in present time the eastern Laptev Sea area and the western East Siberian Sea, where seismic and deformation activity took place from Cretaceous time and has finished in Pliocene.