Kenaf fiber is incorporated in a polybenzoxazine (PBZX) resin matrix to form a unidirectionally reinforced composite containing 20 wt% fiber by a resin transfer molding technique. Two types of benzoxazine monomer are synthesized and used as resin mixtures: benzoxazines based on bisphenol-A/aniline (BA-a) and phenol/ aniline (Ph-a). The effects of varying BA-a:Ph-a ratio in the resin mixture and curing conditions on mechanical properties of pure PBZX resin and kenaf/PBZX composites are studied. The flexural strength of the pure PBZX resin increases with increasing ratio of BA-a:Ph-a, curing temperature and curing time, but the impact strength increases only slightly. PBZX resin has lower water absorption and higher flexural modulus, when compared with unsaturated polyester (UPE) resin. PBZX composites with 20 wt% fiber content have lower flexural and impact strengths, but higher flexural moduli compared with UPE composites with the same fiber content.