Ring-opening polymerization behavior of a model p-cresol aniline-based benzoxazine under various conditions was investigated in detail by (1)H NMR analysis in deuterated DMSO. An improved mechanistic scheme was proposed to explain the observed experimental results. In light of this mechanistic scheme, several bifunctional catalysts were studied, and lithium iodide was found to be a very active and effective catalyst. Lithium cation is the Lewis acid part and effectively coordinates with oxygen or nitrogen atoms and promotes ring-opening of benzoxazines. Iodide ion is the nucleophilic part with good leaving ability and can react with the ring-opened imminium intermediates to prevent its rapid recombination with the phenolate.