In this study, the organo-soluble dodecylamine amine (DDA)-modified reduced graphene oxide (DDA-rGO) was synthesized using two different grafting methods. DDA was covalently bonded with GO sheets by direct amidation processes in the presence of N, N'-Dicyclohexylcarbodiimide (DCC), followed by reduction with hydrazine hydrate to prepare the DDA-modified reduced GO (DDA-rGO1). Analogous DDA-modified rGO (DDA-rGO2) was prepared by modifying GO with DDA in the absence of DCC. The ultraviolet-visible spectra showed that the DMF dispersion of DDA-rGO1 and DDA-rGO2 followed Beer's law and their molar extinction coefficient values were calculated to be 64 and 44 mL mg(-1) cm(-1), respectively. The AFM, TEM, and TGA confirm the higher amount of DDA attached in DDA-rGO1. These fillers with various loading amounts were successfully used to synthesize several composite films using polyurethane (PU) as matrix. All nanocomposites showed excellent improvement in mechanical and gas barrier properties than PU. DDA-rGO1-4/PU with 4 wt% DDA-rGO1 improved the tensile modulus (E) by 204% and reduced O-2 permeability (P) to 84% compared to PU. On other hand, DDA-rGO2-4/PU enhanced the E by 122% and declined P to 80% compared to PU. The DDA-rGO1 demonstrated a better reinforcing efficiency to improve the mechanical and gas barrier properties.