Poly[2-(beta-D-glucosyloxy)ethyl acrylate] (PGEA) was prepared by radical polymerization of 2-(2',3',4',6'-tetra-O-acetyl-beta-D-glucosyloxy)ethyl acrylate (AcGEA) followed by O-deacetylation. Fluorescence measurements revealed that PGEA tended to associate into aggregates in an aqueous medium. The critical aggregation concentration (cac) of PGEA in water was determined by using N-phenyl-1-naphthalamine (PNA) as a fluorescent probe. The dependence of cac on the molecular weight of PGEA and temperature was observed. A copolymer of GEA with a hydrophobic monomer, i.e., stearyl acrylate (SA), was also synthesized in order to increase the hydrophobicity of PGEA and to understand the hydrophobic effect on cac. It was found that the cac of P(GEA-co-SA) was much lower than that of PGEA, and it decreased with increasing ratio of SA in the copolymer. Size-exclusion chromatography (SEC), dynamic light scattering (DLS), and transmission electron microscopy (TEM) measurements indicated that the aggregates have hydrophobic interiors; they were spherical in shape and their sizes varied in a broad range. This phenomenon was explained in terms of a combination of hydrophobic interaction and cooperative hydrogen bonding.