Natural fibers have good properties to be used as reinforcement in composite materials. The main issue is their hydrophilic behavior. So we propose here to investigate the diffusion phenomenon in such fibres. First, a brief characterization of four vegetal fibers has been achieved. We show that all fibers have a similar composition and structure despite their different origin. Then, their moisture diffusive behavior was investigated. The samples were submitted to hygro-thermal aging either in total water immersion at room temperature or in an environmental chamber at 80% relative humidity and 23 degrees C. Various predictive models were used to simulate experimental curves. Results show that all fibers exhibit a similar diffusive behavior in a same environment. In immersion, specimens show anomalous absorption kinetics and Langmuir theory actually describes very well the diffusion kinetics in such conditions, whereas the same fibers follow a Fickian diffusion when they are exposed to vapor during relative humidity aging. (c) 2013 Wiley Periodicals, Inc.