The efficiency of an optical sensor embedded in a composite structure strongly depends on the interfacial adhesion between the optical fiber coating and the surrounding solid material and on the environment humidity. Moisture diffusion can induce a decrease of the mechanical stiffness and strength of organic matrix composites. The present work reports on the study of the interfacial adhesion of an optical fiber embedded in a composite material. A sample composed of optical fibers embedded in an epoxy vinylester resin or polyester resin with glass fibers was studied to evaluate the influence of the water diffusion and the glass concentration on fiber bonding. © 2020, Cefin Publishing House. All rights reserved.