A thin film transistor (TFT) and the manufacturing method thereof are disclosed, and the thin film transistor comprises: a substrate, a gate electrode, a first CuSi.sub.x layer, a gate insulting layer, a semiconductor layer, a second CuSi.sub.x layer, and a source electrode and a drain electrode. The gate electrode is disposed on the substrate, wherein the gate electrode includes the material of copper (Cu). The first CuSi.sub.x layer is disposed between the gate electrode and the substrate. The gate insulating layer is disposed on the gate electrode. The semiconductor layer is disposed on the gate insulating layer. The second CuSi.sub.x layer is disposed between the source electrode and the semiconductor layer and is disposed between the drain electrode and the semiconductor layer, wherein the source electrode and the drain electrode include the material of copper (Cu). The source electrode and the drain electrode are disposed on the second CuSi.sub.x layer. Accordingly, the reliable TFT is provided through providing at last one CuSi.sub.x layer for enhancing the adhesion of copper and silicon and avoiding the diffusion, and the yield is improved as well.