The preliminary results of an ambient-vibration based investigation conducted on the San Ciriaco Belfry in Ancona (Italy) is presented. The assessment procedure includes full-scale ambient vibration testing, modal identification from ambient vibration responses, finite element modeling and dynamic-based identification of the uncertain structural parameters of the model. As the most doubtful parameters, the modulus of elasticity of the masonry is adjusted to achieve the experimental results with numerical model by simple operation