Abstract: Uniaxial deformation-measuring device includes a section of optical fiber equipped with a Bragg grating aligned with the measurement axis, and a test body subjected to the deformations to be measured., this device includes the fixing points for attaching the fiber to the test body. The fixing points are separated by a distance (Lfib) having a variation (?Lfib). When the test body is stressed by the deformation, the effective length (Lce) of the test body has an elongation (?Lce). The length (Lfib) of the section of optical fiber and the effective length (Lce) of the measurement body are such that the longitudinal deformation (?Lfib/Lfib) of the section of optical fiber is strictly greater than the originating deformation (?Lce/Lce) of the test body, thus defining an amplification factor K which is strictly greater than 1 and which is equal to the quotient (?Lfib/Lfib)/(?Lce/Lce) in the first order.