The size-dependent resistive switching (RS) properties of the active region in a 1 x 1 NiN-based crossbar array (CBA) resistive random access memory (ReRAM) are investigated in the range of 2 × 2 μm2 to 8 × 8 μm2. In the forming test, the forming voltage is reduced by decreasing the cell size of the active region. Compared to the 8 × 8 μm2 CBA ReRAM, the forming voltage of the 2 × 2 μm2 CBA ReRAM was reduced from 8 V to 6.2 V. In addition, VSET/RESET and the current for the reset operation are reduced in the current-voltage (I-V) results by reducing the cell size, while the current at a high-resistance state (HRS) is increased. As a result, the current ratio between the HRS and a low-resistance state (LRS) is reduced. On the other hand, the variation of VSET for I-V curves repetitively acquired 100 times is decreased by decreasing the cell size in the reliability test. Further, the current at the HRS for the 2 × 2 μm2 CBA ReRAM is the most stable with the smallest current variation for 1000 s in the retention test. These results show that reducing the active region in the CBA ReRAM structure is effective for improving the reliability of ReRAM cells because it reduces the operating voltage and current as well as the variation of VSET and the current at the HRS.