In this paper we present the design and fabrication of two flexible sensor devices: humidity sensor and ammonia sensor integrated with electronic circuit interface on thin flexible substrate (8 mum). The transducers layout has been optimized by means of numerical simulations. A thin layer of Bisbenzocyclobytene (BCB) is used as dielectric sensitive material in humidity sensor. Conversely a mixed polymer layer based on polyaniline emeraldine base (PANi-EB) is used as sensing conductive polymer for ammonia.