The hydrogen solubility in the CaF2-CaO-SiO2 slag system has been studied to identify and compare the hydrogen dissolution behavior according to basicity and CaF2 content at high temperature of 1 823 K. The hydrogen solubility typically increases with higher CaF2 content across the entire compositional range, but its effect is more pronounced at higher basicity. At low basicity, CaF2 seems to slightly polymerize the slag network increasing the available incorporation sites, where hydrogen can attach and increase hydrogen content in slag. At high basicity, the slag structure is already highly depolymerized and CaF2 addition does not affect the silicate structure, but likely affects the slag hydrogen solubility by lowering the hydroxyl activity. CaO additions lowered the hydrogen content in slag at low basicity and increased the hydrogen content in slag at high basicity. From the temperature dependence of the hydrogen solubility, the dissolution energy of hydrogen in slag was found to be 42.3 kcal/mol.