Two methods of evaluation of the compressive strength of old mortars were developed at the Laboratory of R.C. Structures NTUA. A short description of the two methods as well as some results obtained from their application are reported in this paper. a) The scratch-width method applied in-situ consists of measuring the width of a scratch producted by a devise moving along the surface of mortar joints. The method is calibrated by means of scratch tests and conventional testing of mortars in Laboratory. Thus, the scratch-widths measured in-situ may be translated into compressive strength of mortar. b) The fragments-test method: Small pieces of mortar taken out from old masonries are subject to direct tension by applying a testing method developed at the Laboratory of R.C. The combination of the two methods allows for a rather accurate estimation of the mechanical characteristics of mortars to be introduced in assessment, analysis and redesign of old masonries.