Abstract The glass forming ability and crystallization kinetics of water-quenched GeSe 2GeTeSb 2Te 3 molten alloys were investigated by means of differential scanning calorimetry and X-ray diffraction. The glass-forming region for a cooling rate of the order of 10 3 K/min was deduced and compared with the theoretical glass-forming region obtained, assuming the formation of specific molecular structural units that take into account the chemical short-range order. It was found that easy glass forming alloys lie mostly around the monotectic invariant line joining the eutectic points of the GeSe 2GeTe and GeSe 2Sb 2Te 3 quasi-binary systems. Upon heating crystallization proceeds in one or two stages depending on the composition of the sample. The effective activation energy of the first crystallization peak was obtained. All the results were analysed in the light of the current empirical parametrization of glass forming ability and resistance to crystallization of a supercooled liquid. A new parameter of glass forming ability related to the time needed to obtain a certain amount of sample crystallized at the glass transition temperature was used. From this analysis it is concluded that the best glass formers in that system are compositions in the region near (GeSe 2) 73(GeTe) 15(Sb 2Te 3) 12 molten alloy.