Experimental and numerical investigations are performed to assess the durability of Palmyra natural fiber composites under hydrothermal ageing conditions. The effect of alkali and stearic acid pretreatments is analyzed on the moisture uptake. The natural fiber composite specimens were subjected to accelerated ageing under water and humidity conditions at controlled temperatures between 0°C-75°C. The 4% stearic acid treatment lead to a remarkable reduction in moisture diffusivity. The coefficient of moisture diffusion of different specimens of is calculated using edge correction factor for rectanguloid specimens. The methods presented here can be used to assess and improve the hydrothermal durability of Palmyra fiber composites.