The effect of water absorption damage on the nanohardness and elastic modulus properties of the hemp fibre reinforced unsaturated polyester composites (HFRUPC) have been investigated using the nanoindentation testing. HFRUPC specimens containing 0, 28, 37 and 45 fibre wt.%, corresponding to neat UP, UP/3 layer hemp, UP/4 layer hemp and UP/5 layer hemp, respectively, were prepared and subjected to water immersion tests in a de-ionised water bath at 25 C and 100 C for different time durations. Elastic modulus and nanohardness properties of water immersed specimens subjected to both aging conditions are evaluated and compared alongside dry composite specimens. The elastic modulus and nanohardness properties of HFRUPC specimens were found to increase with the increase in fibre wt.% and decrease with increase in percentage moisture uptake. Nanoindentation is an effective technique to measure elastic modulus and hardness on a nanometer range. Its attractiveness lies largely from the fact that nanomechanical properties can be determined directly from indentation load and displacement measurements. SEM study was also applied to relate the decrease in properties as a result of water uptake in hemp composites.