Bimetallic Pt-Ni nanoparticles (bi-MNPs) have been prepared at room temperature by a wet chemical technique from a micellar solution containing the corresponding metal salts. Co-reduction of the salts produced alloyed particles in bulk quantity. Use of different ratios of the respective metal salts supported the synthesis of tunable compositions of the Pt-Ni alloys. These alloyed bi-MNPs of variable compositions were exploited to Study their catalytic activities towards the reduction of aromatic nitro compounds. The kinetics of the reduction was monitored under different experimental conditions. The catalytic activity of the Pt-Ni bi-MNPs has been found to be superior to the activities of monometallic Pt nanoparticles. Moreover, it was found that the rate of reduction of nitroaromatics is sensitive to the composition of the alloy catalysts. This could be attributed to the electronic effect and the segregation behavior of the material in the alloy. (C) 2004 Elsevier B.V. All rights reserved.