The upcoming Chacao Channel Bridge that will be located atX region in southern Chile, is undoubtedly one of the mostimportant civil engineering projects in Chile and the world.The location of this mega structure is framed and confined byseveral hazard sources, from which the seismic hazard,uniform and local, is one of the most important to consider.One of the basic hazard variables is the evaluation of the siteeffects,due to dynamic amplification of soil or of topographickind. Those effects can increase the seismic demand onspecific areas, and mainly for long span bridges, in which thisaspect is considered as part of the spatial variability effects.This paper describes the main results related with theevaluation of site-effects in the area of the upcoming ChacaoChannel Bridge. The geophysical surveys performed applyingrefraction/reflection techniques as well as ambientmicrovibration analysis are explained and detailed.Predominant periods of soils, ground stiffness anddynamic/topographic amplification are exposed.Results for the north and south access are presented as thebasis for the evaluation of the local seismic demand of thestructural system.