Azobenzene dendrimer E-2, having water-soluble dendrons at the ortho-position in azobenzene, showed novel solvato-chromism with changing the solvent ratio of water/EtOH which is based on the intramolecular hydrophobic interaction due to poly-aryl (ether) dendrons. The thermodynamic parameters for Z-to-E thermal isomerization of 2 also greatly depended on the water/EtOH ratio.