A floating-gate-type organic memory device was designed and fabricated by modifying a thin- film transistor structure. Thin films of plasma-polymerized methyl methacrylate (ppMMA) and plasmapolymerized styrene (ppS) were prepared for use as the functional thin film in an organic memory device. The ppMMA thin film was utilized as both an insulating and a tunneling layer. Two types of memory layers were utilized: (1) ppS and (2) vacuum evaporated Au. The fabricated devices were examined by using current-voltage measurements made using the double-sweep procedure. The memory window and the retention time of the memory devices were comparatively investigated. The device with the ppS memory layer revealed a memory window of 19 V and showed a retention time of over 2 h. We confirmed that ppS could be utilized as a memory layer for a floating-gate-type organic memory device.