AbstractComposites of polycaprolactone (PCL) and vital wheat gluten (VG) were extruded, injection‐molded, and analyzed using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscope, and Fourier‐transform infrared (FTIR). Neat PCL sample was cooled down to −70°C and heated to 150°C, where a glass transition (Tg) emerged at −67.0°C [0.20 J/(g °C)] followed by a melting transition at 56.6°C. At the end of the heating cycle, a cooling cycle started, where the same sample exhibited crystallization transition at 30.1°C. VG exhibited a Tg at 63.0°C [0.45 J/(g °C)]. Data analysis of TGA showed a one‐step degradation mechanism of neat PCL versus multiple steps for the composites, indicating similar molecular structure and physical properties of neat PCL unlike the composites. In nitrogen environment versus air, the degradation activation energy (Ea) of the composites has increased at higher VG levels. From the DSC and TGA data, it is apparent that some physical interaction between PCL and VG was present. The FTIR analysis verified the physical nature of this interaction as opposed to chemical interaction. Proteinase degradation activity on the extruded composites was much higher than the injection‐molded as indicated by higher weight loss in the extruded samples. Published 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008