For the first time, reduced pressure to induce a framework contraction of the microporous titanosilicate ETS-4 is used. A vacuum of 10(-2) Torr decreases the temperature of structural contraction from 200 degrees C to near room temperature and presents a potential alternative to the temperature-induced and anion-controlled molecular gate effect. The dimensions and the reversibility of the temperature- and vacuum-induced framework contractions are evaluated by in situ X-ray diffraction experiments. On the basis of these studies, it is revealed that Na-ETS-4 possesses a more rigid framework than Sr-ETS-4, which discloses a way to control the framework flexibility of ETS-4.