The "El Buey" dam is located at 45Km of Medellin in the NW of Colombia, placed in an area of high seismic activity. This dam is part of the main water supply system of the city. The "Study of seismic vulnerability of El Buey dam", was developed and included analysis of instrumentation records, local geological study, seismic hazard evaluation with EZ-FRISK v6.2 software and subsoil exploration. Static and dynamic laboratory test and numeric analysis were made for evaluation of seismic response of the dam with QUAD4M and PLAXIS V8.1. In this paper, a summary of the executed activities is presented.