Novel benzoxazine monomers containing arylpropargyl ether were prepared, and highly thermally stable polybenzoxazines were obtained by the thermal cure of the monomers. One monomer is a monofunctional benzoxazine, 4-propargyloxyphenyl- 3,4-dihydro-2H-1,3-benzoxazine (P-appe), and the other is a bifunctional benzoxazine, bis(4-propargyloxyphenyl-3,4-dihydro-2H-1,3-benzoxazinyl)isopropane (B-appe). The chemical structures of these novel monomers were confirmed by IR and H-1 NMR. The cure behavior of the monomers, P-appe and B-appe, and the properties of the resulting polymers were studied in comparison with 4-phenyl-3,4-dihydro-2H-1,3-benzoxazine (P-a) and bis(4-phenyl-3,4-dihydro-2H-1,3-benzoxazinyl)isopropane (B-a) as typical benzoxazine monomers without propargyl groups. DSC cure of both P-appe and B-appe showed a single exotherm corresponding to the ring-opening polymerization of oxazine ring and cross-linking of arylpropargyl ether group at almost the same temperature range as P-a and B-a. The T-g values of polybenzoxazines derived from propargyl-containing monomers, PP-appe and PB-appe, were higher by ca. 100 and 140 degreesC than those of typical polybenzoxazines without propargyl groups, PP-a and PB-a, respectively. The storage moduli of PP-appe and PB-appe were maintained constant up to higher temperature for ca. 100 degreesC than that of PP-a and PB-a. The higher thermal stability of the novel polybenzoxazines, PP-appe and PB-appe, than that of the typical polybenzoxazines, PP-a and PB-a, was proved from thermogravimetric analyses.