The main objective of this study was to replace the chemical polymers with natural and renewable polymer and subsequently reducing environmental concerns. In addition, the physical and mechanical properties of composites reinforced with tobacco stalk flour, were studied. For this purpose, the tobacco stalks flour and poly lactic acid contains30:70; 40:60, 50:50 and maleic anhydride grafted polypropylene as a coupling agent, in two levels of 4 wt% and 6 wt% were used as variable factors. The results showed that by increasing the amount of the tobacco stalk flour and reducing the content of PLA, the dimensional stability of the boards was decreased but the dimensional stability of boards made with PLA improved significantly compared to the polypropylene composites. In many cases, the mechanical properties of the composite were increased and even doubled than mechanical properties of the composite made with polypropylene. That's mean; the PLA's natural polymer did not damage the physical and mechanical properties of the wood-plastic composites, but also in some cases improves its properties up to 50% compared with chemical polymers. This natural and renewable polymer is environmentally friendly and the composite can be placed in a group of green composites.