A thin film transistor and a method for manufacturing the same capable of reducing a change in a threshold voltage of the thin film transistor formed on a flexible substrate. The thin film transistor includes: a substrate, the substrate being flexible; a buffer layer having a low dielectric constant from about 1.2 to about 4.0 and formed on the substrate; a semiconductor layer formed on the buffer layer; a gate electrode; first insulation layer formed between the gate electrode and the semiconductor layer; a second insulation layer formed on the semiconductor layer and the gate electrode; and a source/drain electrode electrically connected to the semiconductor layer through a contact hole formed in the second insulation layer. Therefore, the thin film transistor can reduce a change in its threshold voltage, thereby reducing changes in brightness, gray scale, contrast, etc., of light-emitting devices using the thin film transistor.