A series of azobenzene-cored polyphenylene dendrimers have been synthesized. The photoresponsive properties of these dendrimers have been investigated by optical spectroscopy and gel permeation chromatography (GPC). These polyphenylene dendrimers exhibit a photoresponsive behavior upon UV and visible irradiation, resulting in a reversible and appreciable change of the dendrimer structure. Furthermore, the influence of dendrimer generation and degree of branching on the kinetic characteristics of the photoisomerization is discussed. The crystal structures of two precursors and two solvate structures of the first generation are presented.