Variations of the effective activation energy (E_α) throughout the glass transition were determined for 1,2-propanediamine (12PDA), 1,2-propanediol (12PDO) and its solutions of LiBF₄ by applying an isoconversional method to differential scanning calorimetry (DSC) data. For 12PDA, E_α is found to markedly decrease from 660 to 188 kJ mol^—1 throughout the glass transition, whereas 12PDO does not show such drastic change in E_α, which remains at around 145 kJ mol^—1. Although the two simple liquids are similar in molecular structure and size, the cooperative dynamics in the glass transition can be quite different because of differences in the strength or stability of hydrogen-bonding structure between them. We also have discovered that the addition of LiBF₄ significantly affects E_α for 12PDO. The glass transition dynamics are affected more by adding LiBF₄ at an early stage of the glass-to-liquid transition rather than at later stages. As the mole fraction x of LiBF₄ increases, the value of E_α initially increases, but it decreases dramatically during the glass transition. The expansion of cooperativity and its fragmentation, which are reflected in the abrupt change in E_α, can be explained in terms of competition between the hydrogen-bond networks of the alcohol solvent and the ionic interactions due to the added salt. The variability of E_α with temperature is found to correlate strongly with the kinetic fragility.