An excimer fluorescence technique has been applied to the measurement of T-g of ultra-thin polystyrene films. This technique utilizes an excimer-forming molecule with fluorescent emission in two wavelength bands. The intensity ratio of these bands is a sensitive measure of local viscosity. This technique has been applied to five polystyrene films in the thickness range of 25 nm to 200 nm supported on quartz substrates. The observed T-g for the five ultra-thin polymer films was similar to the bulk T-g with no observed dependence upon thickness. Additionally, the T-g determined for each film did not show any dependence upon thermal history.