A TFT and an OLED device are provided. The TFT includes a substrate, a gate, a gate insulator, a source/drain layer, an isolated layer, and a channel layer. The gate is disposed on the substrate. The gate insulator is disposed on the substrate and covers the gate. The source/drain layer is disposed on the gate insulator, and exposes a portion of the gate insulator above the gate. The isolated layer is disposed on the source/drain layer and has an opening to expose a portion of the gate insulator and a portion of the source/drain layer above the gate. The channel layer is disposed in the opening of the isolated layer. Further, the channel layer is exposed by the opening and is electrically connected to the source/drain layer. On the other hand, the OLED device mainly includes a driving circuit and an organic electro-luminescent unit.