In this study, organic memory devices with a single active layer between the two external electrodes were fabricated using an electron-donor type conjugated polymer and an electron-acceptor type small organic molecule. The active layer of the memory device was prepared by blending polystyrene, poly[10-(2'-ethylhexyl)phenothiazine-3,7-diyl], and tetracyanoquinodimethane in 1,2-dichlorobenzene. The device initially showed a low-conductance state (OFF state) in the low-voltage range, and an abrupt current increase, corresponding to the transition to a high-conductance state (ON state), occurred at a certain voltage (V-th). The ON state could be reverted to the OFF state by applying a voltage higher than V-th. The current ratio between the two states was about 10(3) (up to 10(5)). After this transition, the device remained in the ON state even after the applied voltage was removed, and this indicated the nonvolatile characteristics of the device. There was no sharp current degradation in the OFF or ON states for 4500 s of continuous bias. The device-to-device performance fluctuation was measured, and the conduction mechanisms in the ON and OFF states were examined by fitting the data to well-known theoretical models. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 2188-2193, 2012