An element substrate and a display device are provided. The element substrate includes a substrate and an element layer, and the element layer is disposed on the substrate, wherein the element layer includes a plurality of active elements, each of the active elements includes a gate, a gate insulating layer, a metal oxide semiconductor layer, a source and a drain. The gate is disposed on the substrate. The gate insulating layer is disposed on the substrate and overlaps the gate. The metal oxide semiconductor layer is disposed on the gate insulating layer. The source and the drain are disposed on the metal oxide semiconductor layer, wherein the source and the drain respectively include a first layer and a second layer, the first layer is between the second layer and the metal oxide semiconductor layer, and the material of the first layer includes titanium nitride. Thereby, during the process of manufacturing the active elements, titanium atoms are not easy to diffuse into the metal oxide semiconductor layer so that the element substrate and the display device have good reliability.