Mangrove wood particle (MP) of size range 500-1000 microns was thermally modified under inert condition to avoid oxidation at 120 degrees C. The untreated and treated mangrove were compounded with high-density polyethylene (HDPE) at 10 wt%, 20 wt% and 30 wt% in an extruder with twin screw and injection-moulded into rectangular bar shapes for impact tests; fractured surfaces of impact specimens were examined. Also, the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were evaluated. The results of the impact tests showed that increase in fibre loadings gave rise to an increase in peak load and critical stress intensity factor while energy to failure and critical strain energy release rate decreased which signifies improvements in the toughness of the composites. Scanning electron microscopy images revealed that there is stronger adhesion between the HDPE matrix of treated MP than their untreated counterparts. A decrease in the degree of crystallinity (X-c) was noted in the DSC of all composites with treated composites showing higher values ofX(c). TGA showed a slight increment in the degradation peak temperature (T-p) of treated MP and MP/HDPE composites.