The phase-transition behavior of unimolecular dendritic polyethylene amphiphiles with core-shell architecture aqueous solutions was investigated by a Rayleigh scattering (RS) technique. Dendritic polyethylene (DPE)-poly(oligo-(ethylenegylcol) methacrylate) (POEGMA) with a DPE: hydrophobic core and a POEGMA hydrophilic shell was synthesized by the atom-transfer radical polymerization (ATRP) of OEGMA using DPE terminated by the bromine group as a macroinitiator. The fluorescence measurements implied that DPE-POEGMA molecules in aqueous solutions existed as the unimolecular micelles. To understand the phase-transition behavior of dendritic polyethylene amphiphilic unimolecular micelles in aqueous solutions, the temperature dependence of the RS spectra of DPE-POEGMA aqueous solutions under the heating-and-cooling cycle indicated that the heating and cooling processes were reversible but hysteresis existed. The phase transition of DPE-POEGMA aqueous solutions decelerated with increasing levels of PEGylation. DPE-POECMA exhibited a lower phase-transition temperature in D2O than in water.