The present study proposes a methodology to characterize the mechanical properties of synthetic macrofibres, which are used as a reinforcement of new composites applied in civil construction industry. Some standards suggest that this characterization should be performed on original filaments and others propose using the current methodology used to characterise metallic fibres. These recommendations turn difficult the quality control procedure, so it was developed a methodology to characterize the mechanical properties of the macrofibres as they are supplied in the construction site, using the tensile test. In that sense, two types of macrofibres were evaluated obtaining their tensile strength and elastic modulus. Additionally, the macrofibres were mixed with aggregates in order to study how the abrasion affects their mechanical properties. Summing up, the proposed methodology is feasible, especially to estimate the tensile strength allowing its application in ordinary laboratories. Regarding the elastic modulus results, they may be underestimated using this method. Finally, it was observed that the abrasion between the macrofibre and the aggregates during the mixing process compromises the mechanical properties decreasing both the tensile strength and the elastic modulus.