The recently synthesized Engelhard titanosilicate (ETS-10) represents a material which contains in the structure well defined atomic &cellip;O–Ti–O–Ti–O&cellip; quantum wires embedded in a highly insulating siliceous matrix. We report and discuss the UV-Vis spectrum of this material and compare the experimentally determined optical band gap with the results predicted by simple modeling of a titanium oxide semiconductor wire unidimensionally confined by an infinite potential barrier. ©1997 American Institute of Physics.