Carbon supported platinum is commonly used as anode and cathode catalyst in low-temperature fuel cells. The need of modify the chemical characteristics of the supported catalyst has emerged due to several factors, such as reducing the price of the active catalyst and increasing its activity, selectivity, and long-term stability. Thus, pure Pt is now rapidly being replaced by oxide promoted Pt and Pd or Pt-and Pd-based alloy catalysts in low-temperature fuel cells. In addition to the chemical characteristics of the catalysts, many studies on nanocatalysts have been addressed to correlating the catalytic activity with some physical characteristics of supported fuel cell catalysts. This review article examines the role played by metal particle size, inter-particle distance and metal loading on the support in determining the catalytic activity of supported catalysts. (C) 2015 Elsevier B.V. All rights reserved.