Poly(2,6-dimethyl-1, 4-phenylene oxide) (PPO) is a well-known high heat-resistant polymer and miscible with polystyrene. However, it is not miscible with many polymers containing polar groups. In the present study, PPO was nitrated to prepare a nitrated PPO (NPPO) containing polar nitro groups and blended with a copolymer of styrene/acrylonitrile (SAN). Dynamic mechanical analysis (DMA) data showed that NPPO in SAN-rich phase was miscible with SAN, while NPPO in NPPO-rich phase was partially phase-separated from SAN, both over the entire blend composition range from NPPO wt. fractions of 0.1-0.5 investigated for this work. Analyses of Fourier-transform infrared (FTIR) and ultra-violet (UV-VIS) spectra indicated that the miscibility of NPPO with SAN was caused by intermolecular hydrogen bonding of C N group of SAN with OH end-group of NPPO in the NPPO/SAN blends. NPPO's OH end-group, meta-nitro 2,6-dimethyl phenol, was produced during nitration of PPO due to chain scission of aryl ether bond. Besides the intermolecular hydrogen bonding, dipolediplo interaction of the C N and nitro groups resulted in dissociation of the C N dimers and trimers to the C N monomers in the NPPO/SAN blends.