A resistive random access memory (RRAM) and its manufacturing method are provided. The RRAM includes a substrate having an array region and a peripheral region. A plurality of memory cells and a gap-filling dielectric layer overlying the memory cells are located on the substrate and in the array region. A buffer layer only in the array region covers the gap-filling dielectric layer, and its material layer is different from that of the gap-filling dielectric layer. A first low-k dielectric layer is only located in the peripheral region, and its material is different from that of the buffer layer. A dielectric constant of the first low-k dielectric layer is less than 3. A top surface of the first low-k dielectric layer is coplanar with that of the buffer layer. A first conductive plug passes through the buffer layer and the gap-filling dielectric layer and contacts one of the memory cells.