Thermoresponsive micellization of poly(ethylene glycol)-b-poly(N-isopropylacrylamide) (PEG(110)-b-PNIPAM(44)) in water is studied by static light scattering and dynamic light scattering. The critical aggregation temperature of PEG(110)-b-PNIPAM(44) is a little higher than homopolymer PNIPAM, and it depends on the block copolymer concentration, which increases from 33.7 to 38.4 degrees C when the copolymer concentration decreases from 2.0 to 0.20 mg/mL. Above the critical aggregation temperature, thermoresponsive micellization occurs, and the resultant spherical micelles consist of a PNIPAM core and a PEG shell. The block copolymer concentration exerts a strong influence on the size and structure of the resultant micelles. Micellization of PEG(110)-b-PNIPAM(44) at higher copolymer concentration favors formation of narrowly distributed, small, and dense micelles, while large, loose micelles or micellar clusters form at lower block copolymer concentration.