The research work focused on the preparation of biobased eugenol benzoxazine (EUBz) using thiourea as amine resource and their conversion into EUBz‐epoxy (EUBz‐EP) blend matrix and EUBz‐EP blend composites. In the present work, thiourea‐based eugenol‐benzoxazine monomer was synthesized using eugenol as phenolic compound, thiourea as amine resource and paraformaldehyde. The molecular structure of monomer was confirmed by FTIR, NMR, and Maldi mass studies. The thiourea‐based EUBz properties were enhanced by the blending of EP resin and reinforced with varying weight percentages of amine functionalized cashew nut shell carbon ( f‐ CSC). The thermally cured f‐ CSC/EUBz‐EP composites possesses a higher glass transition temperature of 202.9°C when compared to that of the EUBz matrix (104.2°C), which might arise due to the higher crosslinking density resulted from the reinforcement of EP resin with f ‐CSC. In addition, the hydrophobic behavior of the prepared composite materials is improved by blending the EUBz with EP resin and reinforcing with f‐ CSC. The enhancement of the value of contact angle from 80.3° to 105.9° infers the improvement of hydrophobic behavior of f ‐CSC reinforced EUBz‐EP blend composites. The corrosion rate and protection efficiency of 5 wt% f‐ CSC/EUBz‐EP composites exhibits 0.814 (mm/year) and 99.97%, respectively. Data obtained from different studies suggested that the f ‐CSC reinforced EUBz‐EP blended composites can be used in the form of sealants, encapsulants, adhesives, and coatings for different industrial and engineering applications.