In this study, we synthesized dendrimers containing light switchable units, azobenzene group(G4 48-Azo dendrimer). Their chemical structure was verified by using NMR study and UV spectroscopy. To apply to the molecular level switching device or data storage system using Langmuir-Blodgett(LB) film, we investigated the monolayer behavior using pi-A isotherm at air/water interface. The surface pressure was also measured during light irradiation. As a result, the G4 48-Azo dendrimer monolayer showed the reversible photo-switching behavior by the isomerization of azobenzene group in their periphery.