Self-assembled Fe₃O₄ nanoflakes have been synthesized via an ionic liquid-assisted solvothermal method. The obtained Fe₃O₄ nanoflakes are composed of well-aligned nanoparticles with an average diameter of about 15 nm. More importantly, the ionic liquid [C₁₆mim]Cl (1-hexadecyl-3-methylimidazolium chloride) plays a critical role for the self-assembly of nanoparticles into nanoflakes by adsorbing onto the surfaces of the primary Fe₃O₄ nanoparticles.