A series of three-, four-, and six-arm star-shaped poly(N,N-diethylacrylamide)s (s-PDEAM(3), s-PDEAM(4), and s-PDEAM(6), respectively) and PDEAM-block-poly(N,N-dimethylacrylamide)s (s-(PDEAM-b-PDMAM)(3,4,6) and s-(PDMAM-b-PDEAM)(3,4,6)) were synthesized by the core-first group transfer polymerization using core initiators possessing three, four, and six silyl ketene acetals, respectively. The thermoresponsive property of s-PDEAM was compared with that of a linear PDEAM (l-PDEAM), and that of s-(PDEAM-b-PDMAM) and s-(PDMAM-b-PDEAM) was compared with that of linear di- and triblock copolymers, l-PDEAM-b-PDMAM, l-PDEAM-b-PDMAM-b-PDEAM, and l-PDMAM-b-PDEAM-b-PDMAM. Both aqueous solutions of s-PDEAM and s-(PDEAM-b-PDMAM) exhibited lower critical solution temperatures (LCSTs), which were characterized using the cloud point (T-c). For the s-PDEAM with different weight average molecular weights (M(w,MALS)s), T-c very slightly changed within 1.0 degrees C. The thermoresponsive behavior of s-(PDEAM-b-PDMAM) is basically similar to those of l-(PDEAM-b-PDMAM) and l-(PDEAM-b-PDMAM-b-PDEAM). The aqueous solution of s-(PDMAM-b-PDEAM) first shows an LCST-type and then an upper critical solution temperature (UCST)-like (actually not UCST) phase transition, that is, the two-stage phase transition. These thermoresponsive behaviors are confirmed using hydrodynamic radii (R(h)s) by dynamic light scattering measurements.