Memory devices based on composites of polystyrene (PS) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were investigated with bistable resistive switching behavior. Current-voltage (I-V) curves for indium-tin-oxide (ITO)/PS + PCBM/Al devices with 33 wt% PCBM showed non-volatile, rewritable, flash memory properties with a maximum ON/OFF current ratio of 1 × 104, which was 100 times larger than the ON/OFF ratio of the device with 5 wt% PCBM. For ITO/PS + PCBM/Al devices with 33 wt% PCBM, the write-read-erase-read test cycles demonstrated the bistable devices with ON and OFF states at the same voltage. The programmable ON and OFF states endured up to 104 read pulses and possessed a retention time of over 105 s, indicative of the memory stability of the device. In the OFF state, the I-V curve at lower voltages up to 0.45 V was attributed to the thermionic emission mechanism, and the I-V characteristics in the applied voltage above 0.5 V dominantly followed the space-charge-limited-current behaviors. In the ON state, the curve in the applied voltage range was related to an Ohmic mechanism.