A simple seed-mediated growth route is developed to fabricate monodisperse, uniform superparamagnetic Fe(3)O(4) core/gold shell structured nanocomposites with tunable sizes and optical properties, in which gold seed formation and attachment onto the core surface via S-Au covalent bonding proceeds almost simultaneously in the one-pot synthesis. The as-prepared nanocomposite is demonstrated to have a great potential for magnetic resonance imaging (MRI)-guided, focused photothermal tumor therapy under near-IR laser radiation.