Glass formation boundaries in the Al2(SO4)3-AlCl3-H2O system were determined. The glass-formation abilities and crystallization resistance of samples were studied. A glass formation mechanism was suggested. Comparative analysis of the glass-formation abilities of samples of the Al2(SO4)3-Al(NO3)3-H2O and Al2(SO4)3-AlCl3-H2O systems was carried out.