The effect of fibre treatment on the thermal degradation and surface energy characteristics of hemp fibre reinforced unsaturated polyester (HFRUP) composites was investigated by means of a thermogravimetric analyser (TGA) in a nitrogen atmosphere and contact angle measurement. In order to modify the fibre/matrix interface, NaOH treatment and glass fibre hybridisation were employed. HFRUP composites were compared to the unreinforced UP, NaOH treated hemp and glass fibre hybridised hemp/UP composites. TGA test results show that the weight loss for all samples occurred between 200 and 415 °C. The unreinforced UP had a maximum weight loss of 1.011%/°C. For the HFRUP composites, the maximum rate of weight loss was 0.81%/°C. For the NaOH treated and glass fibre hybridised hemp/UP composites, the maximum rate of weight loss was 0.78%/°C and 0.79%/°C, respectively. The effect of fibre treatment on the surface energy of studied samples and their dispersive and polar components were also investigated. Surface energy characteristics obtained from contact angle measurement revealed that for unreinforced UP, the contact angle measured with glycerol is 49.37°. For hemp/UP composites, the contact angle is 76.05°. For NaOH treated hemp/UP composites sample, the contact angle was recorded 78.89°, higher than untreated one. For hemp/CSM/UP specimen, the contact angle was recorded 69.80°. Both TGA and contact angle results indicated that surface treatment and glass fibre hybridisation led to better thermal stability and the wetting behaviour of hemp/UP composites.