A memory device structure includes a substrate, a memory stacked structure, and a spacer. The memory stacked structure is formed on the substrate by stacking a first electrode layer, a memory material layer, and a second electrode layer. The memory material layer has a tilted sidewall, or the memory material layer and the first electrode layer have a tilted sidewall. The tilted sidewall is indented with respect to a sidewall of the second electrode layer. The spacer is disposed on the tilted sidewall.