A novel composite material was prepared by adding marble and granite dust wastes to high density polyethylene matrix. The objective of this work is to study the effect of marble and granite dust particle sizes and its content on the physical and mechanical properties. In this work, the properties of HDPE and HDPE composites were investigated through thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), thermomechanical analysis (TMA), offset yield strength, compression strength and hardness. The results showed that the addition of marble and granite dust improves the thermal and mechanical properties of the HDPE composites. The experimental results of TGA test showed that addition of dust particles increase the degradation temperature by 11 °C and reduces the loss rate of HDPE to 16.71%/min. The TMA results showed that addition of dust particles to HDPE improves the thermal stabilities of the composites. Yield strength, elastic modulus and hardness Shore D were studied. Keywords: Marble and granite dust, High density polyethylene (HDPE), TGA, DTG, DSC, XRF, XRD, Compression, Shore D