Fiber optic sensors for continuous strain measurement in concrete. The determination of load-induced, anisotropic damages under various multi-axial stress conditions requires a strain measurement inside small sized specimens. Therefore, quasi-continuous measuring fibre optic sensors without factory-set protective coating were used. This article explains the measuring principle and shows which measuring configurations are suitable for the existing measuring system in order to obtain exact values, especially in the range of small strains. Sensor fibres and coating material were varied for this purpose and it was investigated which supporting structures could be used to position the measuring sensors in the specimen. The aim was to obtain measurements with at least the same accuracy as the established strain gauge and photogrammetry measurement systems. For this purpose, uniaxial compression and tensile tests on mortar prisms are evaluated and a suitable measuring concept for future multiaxial tests is developed.