The micro- and stereostructures and sequence distribution of methyl methacrylate (MMA)/N-phenylmaleimide (PMI) and styrene (St)-PMI copolymers were studied in detail with NMR spectroscopy. The MMA-PMI copolymer was in a random sequence distribution and the St-PMI copolymer was alternating in structure. Some micro- and stereoinformation of the MMA-PMI copolymers could be obtained from H-1-NMR spectra. The average number sequence length obtained from the copolymer triad try C-13-NMR spectra was in agreement with that calculated from the reactivity ratios measured by an elemental analyzer. From the triad fraction of the copolymer measured by C-13-NMR, the copolymer chain of MMA-PMI was proved to be a one-order Markov chain. More suitable propagation reactions were proposed from the deviation of sequence distribution of the St-PMI copolymer.