Various poly(vinyl chloride) (PVC)/feather keratin (FK) blends were prepared via a solution blending method in the presence of N,N-dimethylformamide as a solvent. The miscibility of the blends was studied with different analytical methods, such as dilute solution viscometry, differential scanning calorimetry, refractometry, and atomic force microscopy. According to the results obtained from these techniques, it was concluded that the PVC/FK blend was miscible in all the studied compositions. Specific interactions between carbonyl groups of the FK structure and hydrogen from the chlorine-containing carbon of the PVC were found to be responsible for the observed miscibility on the basis of Fourier transform infrared spectroscopy. Furthermore, increasing the FK content in the blends resulted in their miscibility enhancement. The thermal stability of the samples, as an important characteristic of biobased polymer blends, was finally examined in terms of their FK weight percentage and application temperature. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 3252-3261, 2011