Polypropylene (PP) composites reinforced with down feather whisker (DFW) with and without surface modification were prepared and characterized through a series of tensile tests. The reaction of isopropyl tri(dioctylpyrophosphate) titanate (NDZ-201) on the surface of DFW was investigated to improve the compatibility between PP and DFW. The chemical reaction between DFW and NDZ-201 was characterized using the attenuated total reflection attachment on the Fourier transform infrared spectroscopy. PP/modified DFW (MDFW) composites showed more uniform whisker dispersion in the PP matrix, higher compatibility and good tensile strength than pure PP and PP/DFW composites. It was worth noting that the Young’s modulus of PP/DFW composites was higher than that of pure PP but lower than that of PP/MDFW composites. Furthermore, the effects of DFW and MDFW on the microstructural and thermal properties of different composites were also investigated, respectively. These results indicated that DFW could be a potential natural reinforcement for the PP matrix achieved with the use of NDZ-201.