The glass transition temperature (T-g) of poly(tert-butyl methacrylate) (PtBMA) Langmuir-Blodgett (LB) films relative to that of spin-coated films on a silicon substrate is investigated by ellipsometry and X-ray reflectively. The T-g of spin-coated films on an oxide-free silicon wafer decreases as the film thickness decreases, which is consistent with the majority of the previous reports in the literature. However, the transition temperature of the LB films is nearly independent of the total thickness, that is, the number of accumulated layers, which is much different from the case for spin-coated films. After sufficient thermal annealing of the LB film, it recovers the thermal transition behavior of the spin-coated film with an equivalent thickness. The layer structure of the LB film is deemed to be responsible for the departure from the behavior of the spin-coated film.