The crystallization kinetics of supercooled Ag-In-Sb-Te liquids (in thick single film) has recently been shown to exhibit a fragile-to-strong crossover (FSC) behavior, which is beneficial to balance the contradiction between fast crystallization rate around the melting temperature (Tm) and good thermal stability (low crystallization rate) nearby the glass transition temperature (Tg). In this work, we fabricated an ultrathin Ag-In-Sb-Te film (∼7 nm) that is confined in a 2D structure. Does this confined ultrathin film exhibit FSC behavior? Focusing on this issue, we studied the crystallization features of 2D confined Ag-In-Sb-Te ultrathin film by using the method of ultrafast differential scanning calorimetry and the viscosity model of generalized Mauro-Yue-Ellison-Gupta-Allan. It was found that, the FSC behavior is presented and enhanced in this confined Ag-In-Sb-Te film. Interestingly, the FSC temperature of this confined Ag-In-Sb-Te is 473 K (∼1.25 Tg), which is equal to that of thick single Ag-In-Sb-Te film, indicating the structural origins of FSC behavior are same in these Ag-In-Sb-Te supercooled liquids, i.e., the FSC behavior stems from liquid-liquid phase transition that is predominantly caused by the increase of Peierls distortions with the competition between short range and medium range cluster. This reveals the crystallization features of ultrathin Ag-In-Sb-Te film, enabling a systematic optimization of the memory-switching kinetics in low-dimensional phase-change device. •The crystallization kinetics of 2D confined AgInSbTe ultrathin film was studied by ultrafast DSC.•A distinct fragile-to-strong crossover kinetics feature was revealed in 2D confined ultrathin AgInSbTe film.•The mechanism of fragile-to-strong crossover in 2D confined ultrathin AgInSbTe film is same to that in single film.