In the present work, a novel physical treatment (PLA coating) of sisal fibres and its influence on the water absorption, static and dynamic mechanical properties of its composites has been presented. The treated sisal fibres were used consisted of alkali treatment and PLA coating to fabricate its polyester-based composites by hand lay-up technique keeping constant fibres content as 20 wt.% . Water absorption analysis was carried out in terms of water uptake (%), and sorption, diffusion and permeability coefficient. In addition, static properties were examined in terms of tensile, flexural and impact test, and dynamic mechanical analysis was performed in terms of storage modulus , loss modulus (E″), damping and glass transition temperature . It was reported that the PLA-coated sisal composites showed the best performance in water absorption, mechanical and dynamic mechanical properties than pure sisal and alkali-treated sisal composites. There were 33%, 49%, 48%, and 27% improvement in water resistance, tensile strength, flexural strength and impact strength, respectively, of PLA-coated sisal composites as compared to that of pure sisal composite.