This study was aimed at identifying the best approach of incorporating nano-graphene (NG) into bagasse/polypropylene composites to enhance their mechanical and physical properties. The composites with different NG contents were produced bymelt compounding in a twin-screwextruder and then by injection molding. The mass ratio of the bagasse flour (BF) to polymer was 15/85 and 30/70 (w/w). Water absorption, thickness swelling, tensile strength, bending characteristics, impact strength and morphological properties of the produced composites were evaluated. In general, applying NG would improve mechanical properties of the composites. The mechanical test results indicated that when only 0.1 wt%of NG was added, tensile and flexural properties reached their maximum values, while the notched impact was slightly decreased. The composites containing 0.1 wt% NG and 30 wt% BF exhibited the highest tensile, flexural and notched impact strength values. Although incorporating NG into the polymer matrix effectively improves mechanical properties, this improvement comes at proper nanofiller loading (0.1 wt%). Addition of NG almost did not change the average water uptake and thickness swelling, compared to the control (without NG) samples. Morphological study confirmed that high contents (0.5–1 wt%) of NG were easily agglomerated. Thermal analysis showed slight increase in thermal stability of WPCs after incorporation of NG particles. In addition, it was found that the effect of BF was notable in material properties of the composites.