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One of the major challenges in the scope of rehabilitation and repair of existing structures is the inspection and analysis of the stability conditions, which includes the detection of the damaged zones, cracking and defects, mechanical characterization of materials and further structural analysis of masonry structures. This diagnosis work is generally carried out not only based on experimental investigation on the laboratory but also by means of in situ nondestructive methods. Sophisticated nondestructive techniques have been developed and improved throughout the years and are applied to various types of structures in distinct fields, namely masonry structures. In this scope, the work presented here deals with a non-destructive approach to make a preliminary diagnosis of an ancient masonry tower, the Quintela Tower, in Vila Real, Portugal. The tower presents a square shape of about 5× 5m2 and has about 30m height and was built exclusively with granite. It presents some distributed cracking and a major concentrated crack near a corner in the north-west corner passing though the units and unit-mortar interface. The stone presents high degree of weathering in some places with detachment of small pieces of material. The inspection of the structure includes the application of GPR and boroscopy to characterize the cross section of the walls and stone slab at the base of the tower. Additionally, natural frequencies were obtained based on dynamic identification with ambient vibration. The characterization of materials (stone and wood) was carried out based on Schmidt hammer for the stone and on the pylodyn and resistograph for the wood …