This work deals with ambient vibration tests performed in the section E of Itaipu Dam in order to estimate modal parameters (natural frequency, modal damping and mode shapes) in operational conditions. The study consists of experimental tests and theoretical modal analysis. The experimental tests were carried out by means of low-frequency accelerometers, placed in different point of the dam. The poly-reference least-squares complex frequency domain (PLSCF) method and covariance-driven stochastic subspace identification (SSI-COV) method have been used to evaluate modal parameters. The modal parameters identified using PLSCF method is in good agreement with the parameters extracted using the SSI-COV method. Furthermore, a finite element model of the section E Itaipu dam has been developed to verify dynamical characteristic, such as natural frequency and mode shapes with the experimental results.