The dilatometric and thermal behaviors such as the thermal expansion coefficient (alpha) and the liquidus temperature (T-1) of Al-Ni-RE (RE=Y, Ce, Gd and Er) amorphous alloys were investigated by a conventional dilatometer and differential scanning calorimetry (DSC). Results show that alpha(exp)/T-1 (defined by theta) has a good positive correlation with glass forming ability (GFA) in Al-based amorphous alloys, where alpha(exp) is the average linear thermal expansion coefficient. A similar phenomenon is also found in Gd- and Cu-based amorphous alloys. Based on the free volume model, it is found that the amorphous alloy which exhibits better GFA contains less free volume. Consequently, the parameter theta can be applied to predict the GFA in the system with same main element. (C) 2009 Elsevier B.V. All rights reserved.