Electrostriction of tactic polymethylmethacrylates in response to step-on and step-offdc-fields was investigated in the field strength range from 1 to 5 MV m−1 at room temperature; one example of electrostriction under sinusoidal field is given. Three principal retardation time regions were found: τ1=1.5 s, τ2=30 s, and τ3=140 s, each field strength independent. The retardation strengths belonging to these electrostrictive processes depend on tacticity. The low frequency limit of the electrostrictive volume compliance for the investigated PMMA is δ a =−1.2×10−15 m2 V −2 for atactic, δ S =−2.3×10−14 m2 V −2 for syndiotactic, and δi=−4.5 × 10−14 m2 V −2 for isotactic PMMA.