Several organic alkanes containing sulfur or nitrogen atoms with different chain lengths and active functional groups were chosen to modify the surface of aluminum powder and these were found to play the role of a soft interphase in an aluminum powder-filled polyurethane (PU) composite system. The surface microstructures of these organic molecules adsorbed onto aluminum were studied using Fourier transform (FT) surface enhanced Raman scattering. The results obtained from spectral analysis showed that these molecules were chemisorbed onto the aluminum surface through S or N atoms to form assembled films because of their strong co-ordinating ability with the metal. At the same time, they act as coupling agents between the PU and aluminum powder through the active functional groups, such as -COOH, -OH, -NH2, etc., present on these molecules. The stress-strain characteristics of aluminum powder-filled PU composites in which aluminum powder was pretreated or untreated were determined and compared. The data showed that the treated aluminum powder-reinforced PU composites possessed a higher tensile strength and higher elongation than those of the untreated systems.