A two-dimensional self-assembly of uncapped Ag nanoparticles was prepared at the air-water interface. In the experiment, ethanol was added into the Ag-based colloid to reduce the surface charge density on the nanoparticles and the air-water interfacial energy, leading to the nanoparticles adsorption and assembling at the air-water interface. It was found that the array structure was controllable. The ordered nanoparticle array could be changed to a fractal structure by varying gradually the amount of the added ethanol. Moreover, it was demonstrated that the assembly was sensitive to the surface charge density on the particles, the Debye length in the colloid and the interfacial tension between nanoparticle/water (air). (C) 2008 Elsevier B.V. All rights reserved.