 Construction of the Palma de Mallorca Cathedral dates to the beginning of the XIVth century. This cathedral represents an excellent example of the gothic style in Spain despite several modifications due to structural problems. Because of the observed inner structural deformations, special attention was focused on determining the role of the flying buttress by measuring the acting stresses in one of them. The in situ stresses have been experimentally determined using the Hole Drilling technique. This technique allows for the determination of the principal stresses and their directions in the stone masonry. This study presents the applicability of the Hole Drilling technique on flying buttresses as structural elements. In this sense, the paper is a very specific and original case study of rock assemblies.