The effects of thickness of a-Si thin films on the resulting microstructure of metal-induced laterally crystallized (MILC) poly-Si and electrical characteristics of MILC low temperature poly-Si (LTPS) thin film transistors (TFTs) were investigated. The TEM images revealed a double-layer structure in the 1000-Å MILC poly-Si thin film. However, for the 400-Å MILC poly-Si thin film, there were single-layer grains within the thin film layer. The reason has been ascribed to the geometry restriction in the crystallization procedure. The average mobility of fabricated MILC LTPS TFTs with active layer thickness of 400 Å showed a little higher than that with 1000 Å active layer. Moreover, the MILC LTPS TFTs with active layer thickness of 400 Å exhibited better electrical uniformity than those with 1000 Å active layer either in threshold voltage or field-effect mobility. The reason should also be attributed to the different crystalline structures within the two thin-film layers.