This paper aims to develop new natural fiber-based composite material for antenna and microwave applications. The biocomposite material has been fabricated from natural flax fiber fabrics and polymer resin using the vacuum infusion manufacturing process. Dielectric properties of the developed material were obtained by microwave characterization using the free-space measurement method over a wide frequency range (2GHz-16GHz). The NRW technique was used to extract the dielectric properties of the developed biocomposite. A dual-band microstrip antenna for 2.45/5.2-GHz WLAN applications was modeled, and fabricated by a screen printing process. Measurement and theoretical investigations show a good agreement and validate the concept of a biosourced antenna on a natural fiber-based substrate.