This paper describes the influence of fibre length, fibre beating and hygrothermal ageing on tensile strength (TS), Young’s modulus (YM), failure strain (FS) and impact strength (IS) of Kraft fibre reinforced polypropylene (PP) composites. TS, YM and IS of composites were found to decrease and FS increased with decreasing fibre length. Modest levels of fibre beating increased the TS of composites, which is believed to be due to improved interfacial bonding. During hygrothermal ageing, the diffusion coefficient increased with increased ageing temperature. Composites without coupling agent showed higher water uptake and diffusion coefficient than those with coupling agent. TS and YM were found to decrease for hygrothermal ageing due to fibre damage and reduced fibre matrix interfacial bonding, whilst FS and IS were found to increase due to the plasticizing effect of water.