Initial hydration and setting properties were investigated to develope manufacturing processes of gypsum wall board from flue gas desulfurized gypsum(FDG). Setting time and ΔT were measured in the presence of accelerator such as, K₂SO₄, Na₂SO₄, and MgSO₄. The hydration rate of FDG was markedly enhanced in the case of 21% addition of 5%-K₂SO₄. ΔT was gradually increased with the increasing of added amount of 5%-K₂SO₄. The adherence strength could be increased due to the promoted formation of slender and longer needle-like crystals by K₂SO₄.