Fibre Bragg Gratings (FBGs) are optical strain gages manufactured directly inside the fiber core. They provide several advantages with respect to conventional strain gages. In particular it is possible to put several FBGs along the same fibre (multiplexing), they are immune to corrosive environments and to electromagnetic interferences. They can be embedded in almost all types of materials and are very useful in Structural Health Monitoring. An innovative approach for testing specimens in this area is reported in this work. An aluminium alloy 2024-T3 CT specimen has been manufactured with one small feed-through hole and a superficial groove. Two FBG sensors, multiplexed on the same fibre, have been glued one inside the hole and one inside the groove. Fatigue test has been carried out monitoring the crack length both with standard measure system and with the FBG strain sensors placed in front of the crack tip.