Water resistance, mechanical properties, and limiting oxygen index (LOI) of wood plastic composites (WPCs) and neat polypropylene filled with different amounts (3, 6, and 9% by weight) of dolomite powder and wood flour (15 and 30 by weight) were investigated. Wood flour, dolomite powder, polypropylene, and wax were dry-mixed in a high-intensity mixer to produce a homogeneous blend. This blend was then compounded in a laboratory-scale single screw extruder. Test specimens were produced by injection moulding process from the pellets dried to moisture content of 1%. The thickness swelling and water absorption of the dolomite polypropylene composites (DPCs) and WPCs slightly increased with increasing dolomite powder content but the differences were not significant. The flexural modulus and tensile modulus of the WPCs and DPCs increased with increasing dolomite powder content while the flexural strength and tensile strength slightly decreased. The LOI of the WPCs and DPCs increased with increasing dolomite powder content, which extended the times to ignition of WPC and polypropylene. Based on the findings obtained from the present study, it can be said that 6 wt% dolomite powder is the optimum amount in the manufacture of WPC and DPC.