The use of plant fibre-reinforced composites in various industrial applications has gained significant attention due to their sustainability, cost-effectiveness, and environmental benefits. However, one of the critical challenges limiting their widespread use is the susceptibility of these materials to moisture absorption, which can affect their mechanical properties and longevity. This study investigates the moisture absorption rate and diffusivity of plant fibre-reinforced composites, with a particular focus on the influence of different fibre types, matrix materials, and environmental conditions. The moisture absorption tests were conducted according to standard methods, and the rate of absorption and diffusivity were analyzed using Fick’s law of diffusion. The results show that fibre type, matrix material, and environmental humidity significantly affect the moisture uptake behavior of the composites. The study provides insights into the factors influencing the moisture resistance of plant fibre-reinforced composites and offers recommendations for improving their performance in moisture-prone environments.