A new type of hydrogen sensor based on a side-polished fiber Bragg grating (FBG) coated with thin palladium film was demonstrated experimentally. The used FBG with the reflectivity of 90% is fabricated in a hydrogen-loaded single-mode fiber (SMF-28) by using the phase mask writing technique of a KrF excimer laser. The experimental results show that proposed sensor can be applied for hydrogen concentration measurements. (C) 2007 Elsevier B.V. All rights reserved.