A PEG-based amphiphilic polymer bearing two aliphatic double chain moieties was prepared. Its diluted aqueous solution properties were studied by viscometry, dye solubilization and rheology. At concentrations lower than (6-8)x10(-3) g/mL ring-shaped macromolecules were formed due to intrachain hydrophobic interactions. At concentrations about (6-8)x10(-3) g/mL a formation of "flower" type aggregates took place. 1,6-Diphenyl-1,3,5-hexatriene solubilization was used to prove the existence of hydrophobic domains and a critical aggregation concentration of 7x10(-3) g/mL was determined. The peculiar viscosity profile and the rheopectic behavior of the amphiphilic polymer were attributed to the existence of aggregates and to a temporary network formation during deformation, respectively.