The purpose of this study is to find the optimum conditions, including the type and concentration of solvent, and the solid/liquid ratio, for the extraction of calcium from Paper Sludge Ash (PSA). Solvents with different properties are divided into the following three groups to conduct the calcium extraction experiments: acid (acetic acid and hydrochloric acid), ammonium salt (ammonium chloride and ammonium acetate), and other (sodium citrate and water). The maximum efficiency of calcium extraction using acid is 54% at a concentration of 0.7 M and solid/liquid ratio of 1:25, while ammonium salt and sodium citrate extract calcium up to 30% and 28%, respectively, at a concentration of 0.3 M and solid/liquid ratio of 1:50.