Benzocyclobutene- (BCB-) functionalized benzoxazine (BOZ) monomers and resins have been successfully prepared. BCB-functionalized BOZ monomers were synthesized by the reaction of 4-aminobenzocyclobutene (AMBCB), phenol and paraformaldehyde or by the reaction of 4-hydroxylbenzocyclobutene (OHBCB), arylamine, and paraformaldehyde in toluene under reflux. Fourier transform infrared spectroscopy (FTIR), H-1 and C-13 nuclear magnetic resonance spectroscopy (NMR) are used to characterize the structure of the monomers. The monomers possess two kinds of ring-opening polymerizable functional groups of BCB and BOZ. So the monomers can be cured at proper temperature to prepare highly cross-linked resins. The polymerization behavior of the monomers is studied by differential scanning calorimetry (DSC) and FTIR DMA study demonstrates that these polymers show high storage moduli which can be maintained in a wide temperature range up to 300 degrees C and high T-g at ca. 350 degrees C. The TGA study shows that the cured resins possess good thermal stability.