Polyethylene imines (PEIs) having 4-butylazobenezene group through methylene spacer groups were prepared, and their thermal as well as photochemical properties was investigated. PEI104 having longer methylene spacer was found to form an out-of-plane structure by heating into an isotropic phase and following cooling. The photochemical control of the molecular orientation of PEI104 between in-plane and the out-of-plane structures could be achieved by combination of thermal and photochemical processes.