Flexible resistive switching memory device is an excellent option for future high density memory and flexible electronics applications. Here, bipolar resistive switching behavior in Al/HfOx/Au resistive random access memory (RRAM) devices fabricated on ultra-flexible polyimide substrates is demonstrated. These devices can be programmed at read-write voltages as low as 0.18 V with on-off current ratios (Ion/Ioff) of 18, resistance ratio of ∼41 in high and low resistance states (HRS & LRS) and stable set and reset voltages over 16 cycles of operation. The mechanism of resistive switching in these devices is explained with help of filament formation and rupture process due to oxygen vacancy and oxygen ions migration. Ohmic conduction prevails in HRS and LRS whereas conduction mechanism is dominated by space charge limited conduction (SCLC). These flexible RRAM devices could be an excellent option for future high density memory applications. © 2016 IEEE.