Well defined A-B-A stereoblock polymers with atactic poly(N-isopropylacrylamide) as a hydrophilic block (either A or B) and a water-insoluble block consisting of isotactic poly (N-isopropylacrylamide) were dispersed in water to form, depending on the chain composition, spontaneously micelles of different morphologies. The structures of the A-B-A stereoblock polymers were carefully characterized using light scattering methods, microcalorimetry, and turbidity. The self-organization and thermally induced phase separation of the stereoblock polymers is strongly affected by the block sequence but not notably affected by thermal history of the polymer solutions. Both flower-like and coil-like branched micelles were observed. Thermal behavior of these is different. However, all polymers form colloidally stable aggregates at elevated temperatures.