Alternating copolysiloxane with both electron donor terthiophene and electron acceptor perylenediimide derivative pendants (PTSi-alt-PDISi) is synthesized successfully. The polymer exhibits high decomposition and glass transition temperatures, good film-forming ability, and high morphological stability. The estimated HOMO and LUMO energy levels of PTSi-alt-PDISi are -5.77 and -3.90 eV, respectively. The fabricated memory device with the configuration of ITO/PTSi-alt-PDISi/Au(Al) shows nonvolatile write-once-read-many-times (WORM) memory characteristics. Its turn-on threshold voltage is 1.7 V, while its ON/OFF current density ratio is around 104 in ambient atmosphere. The well-defined memory property of PTSi-alt-PDISi is attributed to the transition of the pendant terthiophene and perylenediimide groups from the disoriented state to the ordered face-to-face conformation at the threshold voltage and the charge transfer interaction between pendent terthiophene donor and perylenediimide acceptor moieties, which are confirmed by XRD patterns and fluorescence emission measurement. This suggests that the new donor-acceptor polysiloxanes have potential applications in the field of memory devices.