Electrostrictive dilatations in the order of 10−13m are measured in dielectric crystals by an interferometric method based on the Michelson interferometer. The electrostriction constants &ggr;1111of quartz, diamond, and LiF are found to be (−0.6±0.2), (+0.17±0.03), and (−7.9±0.8) 10−21m2/V2, respectively.