To obtain a new benzoxazine derivative capable of giving a polymer having good physical characteristics as a resin, such as strength and elastic modulus, to provide a method for producing the same, to obtain its polymer and a polymerizable composition capable of giving the polymer.

The benzoxazine derivative is expressed by formula (I) or (II) (R1 is H or methyl; R2 is a 1-20C straight chain or branched chain alkyl which may contain hydroxyl group, a 1-20C straight chain or branched chain alkenyl which may contain a hydroxyl group or a 1-20C straight chain or branched chain alkynyl which may contain a hydroxyl group; R3 to R7 are each H, an aromatic ring or a 1-20C straight chain or branched chain hydrocarbon residue which may contain an aromatic ring; R8 is an aromatic ring, O, a 1-20C straight chain or branched chain hydrocarbon residue which may contain an aromatic ring or a direct bond; and X is O or NH). The method for producing the derivative is provided. The polymerizable composition contains the derivative. The polymer is obtained from the composition.