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The recovery of boron from borax sludge by solid−liquid extraction was investigated using 23 factorial experimental design. Distilled water and sulfuric acid were used as extraction solvents. The effects of solid-to-liquid ratio, reaction time, and reaction temperature were investigated for extraction with distilled water. The effects of solid-to-liquid ratio, reaction time, and solvent concentration were investigated for extraction with sulfuric acid. The interaction among the operating parameters and their relative significance were studied. Regression equations were established for both solvents, and the extraction was represented as a function of response variables. The accuracy of equations was verified by Fisher's adequacy test. It was found that the most effective parameter for the extraction process was solid-to-liquid ratio for both of the solvents. Maximum boron oxide extraction efficiency was obtained under the following working conditions:  solid-to-liquid ratio, 1/120 g/mL; reaction time, 60 min; reaction temperature, 75 °C for distilled water; and solid-to-liquid ratio, 1/120 g/mL; reaction time, 60 min; solvent concentration, 1%, v/v; reaction temperature, 75 °C for sulfuric acid.