The effects of -caprolactam on tensile properties, morphology, thermal degradation, and swelling behavior of recycled high-density polyethylene–chicken feather fiber composites (r-HDPE/CFF) were studied. The r-HDPE/CFF composites were prepared using Brabender Plasticorder at 160°C and a rotor speed of 50 r min^-1 for 6 min. The r-HDPE/CFF/-caprolactam composites exhibit higher tensile strength, modulus of elasticity, and final decomposition temperature, but lower mass swell percentage and elongation at break than r-HDPE/CFF composites. Scanning electron microscopic morphology showed that the CFF was more widely dispersed in the r-HDPE matrix with the addition of -caprolactam as a coupling agent. It was also found that the addition of -caprolactam offers better thermal stability in r-HDPE/CFF/caprolactam composites than r-HDPE/CFF composites.