Samples of polyethylene-1.4-cyclohexylenedimethylene terephthalate glycol (PETg) with different filler contents were prepared by a master batch process. The intercalated dispersion state of montmorillonite (MMT) was characterized using X-Ray Diffraction. Two different sample series are put in evidence with different basal distances (3.31 and 3.48 nm). The influence of nanofiller on alpha and beta relaxations was studied by Dielectric Relaxation Spectroscopy and Differential Scanning Calorimetry. The use of these two techniques allowed us to determine accurately the fragility index m at the glass transition temperature T-g. For T-g, m, the Kauzmann temperature T-k, and the relaxation time at T-g tau(T-g), we showed a decrease of the values more important for 3.48 nm basal distance than for 3.31 nm. The beta did not seem affected in its apparent activation energy E-a by the MMT addition. POLYM. ENG. SCI., 49:836-843, 2009. (C) 2008 Society of Plastics Engineers