The swelling and exfoliation behavior of protonated layered oxides using an organo-phosphonium base, tetrabutylphosphonium hydroxide (TBPOH), was examined for the first time. The action of the aqueous solution induced massive interlayer expansion up to ∼100-fold. The swollen crystals were immediately broken and completely exfoliated into unilamellar nanosheets in 1–2 h by shaking.