The role transition of poly(N-isopropylacrylamide) ionic microgels (PNI microgels) in dispersion polymerization by changing the monomer type was investigated in this work. Firstly, PNI microgels with different diameters were prepared by precipitation polymerization. Then they were respectively employed to the dispersion polymerization of glycidyl methacrylate (GMA) and styrene (St) in methanol. Finally, poly(glycidyl methacrylate) (PGMA) and polystyrene (PS) nanoparticles were obtained. The morphology, thermo-sensitivity and element analysis of PNI microgels and these polymer nanoparticles were characterized. It indicated that GMA polymerized inside the microgels while the polymerization of St occurred outside the microgels. This phenomenon demonstrated that the PNI microgels acted as seed for the polymerization of GMA while turned into particulate stabilizer for the polymerization of St. The mechanism of the role transition of PNI microgels from seed to particulate stabilizer was discussed. It revealed that compatibility and chemical interaction between PNI microgels and monomers contributed a lot to this role transition.