The LiNbO3 optical intensity modulator is a promising key device in global optical communication systems which demand high reliability. Although performance of the modulator has been considerably improved to meet practical use, there remain problems related to reliability issues such as unpredictable fluctuation of drift phenomena. In this regard, our recent experimental data on the fabrication of Ti:LiNbO3 modulators are presented here to clarify problems in the device characteristics caused by the device materials. At present, there is little understanding of the origins and mechanisms of the fluctuations, and the estimation and assurance of device quality throughout the long term are difficult. In order to obtain as great a reliability as possible, screening tests for all produced devices are needed.