The ambient vibration test was performed for Namhae Bridge to determine the dynamic parameters of major interest in structural dynamic problems, such as natural frequencies and mode shapes. The reponse signals of Namhae bridge were measured at nine stations in northern half(Hadong side) of the bridge. At each station two accelerometers were attached at each edge of the cross section to measure vertical and torsional natural frequencies. Using FIT algorithm, natural frequencies and mode shapes could be determined from measured data. For the purpose of comparison, numerical natural frequencies are obtained from the two-and three- dimensional mathematical model using finite element method. The computed two-and three-dimensional frequencies and mode shapes show good aggrement with the experimental results. In ambient vibration test bridge was vibrated by random traffics and wind and there is no requirement for traffic control and test procedure is relatively simple. The recording time is so long as to obtain high resolution. Consequently, closely located resonant frequencies could be found.