In this study, the effects of chemical foaming agent and nanoclay on the physical, mechanical, and morphological properties of composites based on HDPE and WF were described. To meet this objective, the nanoclay, HDPE and the coupling agent were compounded and granulated and mixed with WF and blowing agent in a twin-screw extruder. Consequently, the foaming process was completed in the injection stage. The amount of WF was fixed at 50 wt% for all samples. For nanoclay (organomodified montmorillonite) and CBA (azodicarbonamide), different levels of 0, 2, 4, 6 per hundred resins (phr) and 0, 0.5, 1, 1.5 phr were considered, respectively. Results indicate that the cell size and the average cell density of samples increased with the increase in the chemical foaming agent content. However, on addition of nanoclay to HDPE/WF composite foams, the cell size was decreased and their cell density increased. SEM confirmed that the chemical foaming agent and nanoclay contents had significant influence on density reduction of foamed composites. Finally, by increase in the chemical foaming agent content, the tensile modulus decreased and the water absorption and thickness swelling of HDPE/WF nanocomposite increased. The nanoclay dispersion quality is quite an important factor for the physical and mechanical properties of both foamed and unfoamed wood plastic nanocomposites. It was found that the optimal condition was attained by incorporating 0.5 phr foaming agent and 4 phr nanoclay in composite formulation.