The present work describes the preparation of alkali‐treated chicken feather fiber (CFF)‐reinforced cardanol‐based polybezoxazine‐epoxy (CFF/PCBz‐Ep) composites for dielectric and antimicrobial studies, which can be used for antimicrobial corrosion resistant materials for coatings and low‐k applications in future. In this work, a new, more flexible cardanol‐based benzoxazine monomer was taken and it was blended with epoxy resin along with varying weight percentages of CFF to get livestock chicken feather fiber (reinforced cardanol based polybennzoxazine‐epoxy (CFF/PCBz‐Ep) composites. Further, different analytical techniques such as, FTIR, DSC, TGA, XRD, SEM, and TEM, and dielectric analysis have been used to confirm the molecular structure, thermal, dielectric, morphological, and dielectric properties. Data obtained from different studies confirm that the composites show the enhanced glass‐transition temperature (Tg), decreased dielectric values, reduced dielectric loss, improved char yield, and thermal stability compared to those of the neat cardanol‐based polybenzoxazine‐epoxy polymer matrix. In addition, the composites show the significant decrease in the value of dielectric constant than that of the neat cardanol‐based polybenzoxazine‐epoxy and cardanol based polybenzoxazine matrices. The increased Tg, decreased dielectric values, reduced dielectric loss, better char yield, and thermal stability may be explained due to the formation efficient adhesion between alkali‐treated feather fibers and the polymer matrix. Furthermore, the CFF‐reinforced cardanol‐based polybenzoxazine‐epoxy (CFF/PCBz‐Ep) composites show better antibacterial properties when compared to that of the neat cardanol‐based poly benzoxazine‐epoxy (PCBz‐Ep) matrices, which might be due to the amino acids present in the alkali treated CFF in CFF/PCBz‐Ep composites. POLYM. COMPOS., 40:4142–4153, 2019. © 2019 Society of Plastics Engineers