The activation energy (E) of the glass transition and the heating-rate dependence of the glass transition temperature (T-g) of Se glass were determined using differential scanning calorimetry (DSC) technique. Non-isothermal measurements were performed at different heating rates beta (2-99 K/min). The heating-rate dependence of T-g was used to investigate the applicability of different theoretical models describing the glass transition. The application of Kissinger and Moynihan et al. models to the present data led to different values of E for different heating-rate regions. This behavior was attributed to the strong heating-rate dependence of the activation energy of the process. The activation energy of the glass transition was determined by analyzing the data using isoconversional methods: Kissinger-Akahira-Sunose (KAS), Friedman and Vyazovkin methods. A strong variation of the activation energy with the degree of transformation (alpha) was observed in the present sample indicating a complex transformation process of the glass transition. (C) 2008 Elsevier B.V. All rights reserved.