Heterogeneous catalysts normally consist of small metal particles dispersed on a high surface area porous support. Traditional methods, such as wet-chemical processing, can produce metal particle catalysts as small as several nanometers, but these methods cannot precisely control the size of the catalytic nanoparticles and disperse them homogeneously within the porous substrates. In addition, heterogeneous catalysts cannot selectively convert specific molecules in the reactant mixture to catalyze only desired reactions. Novel approaches are required to synthesize stable metal nanoparticles catalysts with tightly controlled sizes to further advance the knowledge of their unique size-dependent catalytic behavior. Recently, atomic layer deposition (ALD) has been used to prepare highly active, highly dispersed metal nanoparticles. In this presentation, we will introduce some examples of nanostructured catalysts prepared by ALD, such as Pt nanoparticles, Ni nanoparticles, Pt-Co bimetallic nanoparticles, and CeO₂ doped TiO₂ nanoparticles.