The longitudinal strains (εx) of the core and the skin layers in glass fiber reinforced plastic (GFRP) cross-ply composite laminates are analyzed using embedded optical fiber sensors (OFSs) of absolute extrinsic Fabry—Perot interferometer (A-EFPI). Foil-type strain gages (SGs) bonded on both upper and lower surfaces of a specimen are employed for comparison of the strain measurement on the surface. It has been shown that the values of εx in the interior of the skin layer and the core layer measured by embedded A-EFPI sensor are lower than those of the specimen surface measured by SGs. Experimental results agree well with those from finite element analysis based on a shear lag model. Optical microscopy observation of the damage behavior around the fiber sensor by the thin-sectioning technique shows that reinforcing glass fibers protect the OFS embedded in the 0 ° skin layer, whereas the formation of transverse cracks in the 90 ° core layer substantially reduces strains at the failure of OFS embedded in the core layer.