Chuyskoe earthquake, which occurred on September 27, 2003 in Altai region, was the strongest one in history of this region. Results of the earthquake confirm high (M=7.5) seismic hazard of Altai-Sayany region. System of seismic stations has made it possible to record shocks. Positions of the main shock and its aftershocks have been noted. Development of seismic activity has been described. Investigations of seismic process in Chuyskaya-Kurayskaya zone before and after Chuyskoe earthquake have been performed. Depth of the aftershocks has been determined. Seismic activity have been noted in upper part of earth crust. Durability of the activity has been discussed.
