Three fluorinated benzoxazines (14-16), which cannot be synthesized by the traditional one-step approaches, were synthesized by a three-step procedure using fluorinated aromatic diamines (2-4) as starting materials. The structures of the monomers were confirmed by H-1 NMR, IR, and high-resolution mass spectra. The low dielectric thermosets, P(14-16), were prepared by ring-opening of (14-16). IR analysis was utilized to monitor the ring-opening reaction of (14-16) and to propose the structures of P(14-16). The thermal and dielectric properties of P(14-16) were studied and compared with a nonfluorinated polybenzoxazine P(13), which is derived form the ring-opening of 2,2-bis(4-aminophenoxy)phenyl)propane (1). Besides, the structure-property relationship of the P(13-16) is discussed. According to T-g measurement, the ortho-positioned CF3 substituents impart greater steric hindrance for ring-opening of benzoxazines than CF3 substituents of hexafluoropropane. Incorporating a biphenol F-based benzoxazine, (F-a), into fluorinated benzoxazines (15-16) can dilute the effect of ortho-positioned CF3 substituents on steric hindrance, leading to a higher crosslinking density and consequently a higher Tg.