A memory device includes a first electrode, a second electrode and a variable resistance layer. The second electrode includes a metal. The metal is more easily ionizable than a material of the first electrode. The variable resistance layer is disposed between the first electrode and the second electrode. The variable resistance layer includes a first layer and a second layer. The first layer has a relatively high crystallization rate. The second layer contacts the first layer. The second layer has a relatively low crystallization rate. The first layer and the second layer are stacked along a direction connecting the first electrode and the second electrode.