The main purpose of this study is to investigate experimentally granite masonry specimens as well as its constituent components, granite stone units and cement mortar, separately under compression so that the results can be used for numerical modeling and analysis of granite masonry structures. The compressive behaviour of granite stone units and cement mortar are characterized and their effects on the strength and deformation characteristics of the masonry structure are examined. The experimental results indicate that granite stone specimens exhibit high peak strength values and very fragile behavior when subjected to compressive loading. The stress-strain relation of the mortar specimens show a strain hardening behavior with more ductility than the granite stone. The strength of granite masonry is much higher than the mortar but less than the average strength of the granite stone units. By using an in-situ optical technique called Digital Image Correlation, quantitative measurements of strain localization in granite masonry are achieved in both deformation and failure modes. It was found that cracks initiated at the vertical mortar joint interface and formed multiple shear bands. Further deformation occurs by extending the shear bands into the mortar joint layers, and finally the granite unit split vertically due to the laterally biaxial tensile force induced by the confinement effect of themortar joints. © 2009 ASCE.