The elevated part of Santiago Metro Line 4 has been built in 2004/2005. The viaduct has a total length of 7 km. The prestressed concrete deck is made of independent spans with a typical length of 35 meters. Each span consists of a U-through section carrying two tracks. The viaduct of the Metro line 4 in Santiago of Chi Ie supported well the violent shaking that occurred during the 2010 February 27th earthquake, without interruption of operations. The earthquake of a magnitude 8.8 has an epicenter located 320 km far from Santiago de Chile. The peak horizontal acceleration registered at ground level in Santiago was 0.27g. The paper presents the viaduct design: spans distribution, cross section, segments distribution, and anti-seismic devices. This paper discusses the condition of the viaduct after the earthquake and includes the diagnosis and expertise. The paper finally presents the repair process and works. The expertise concluded that minor disorders were rational due to the fact that acceleration registered at ground level in Santiago de Chi Ie was very close to the nominal design value. The disorders are located on piers and concern mainly the mortar of elastomeric bearings. and spoiled concrete on shear keys.