Nickel nanoparticulate catalysts supported on hollow Al2O3 ball (<3 mu m in diameter) have been prepared by spraying a mixed solution of nickel and aluminum nitrates in atmospheric pressure plasma. A wall of each ball (ca. several 10 nm in thickness) consisted of uniformly dispersed oxide bricks of ca. 30 nm sizes, which were identified as densely packed NiO, NiAl2O4 and Al2O3 crystallites. Highly dispersed Ni particles (<10 nm in diameter) have been formed on the ball surfaces by H-2 reduction of NiO crystallites, surrounded by the nano-sized oxide bricks of NiAl2O4 and Al2O3. A catalytic activity of the Ni catalyst thus prepared for methane steam reforming reaction was tested from a viewpoint of the application to fuel processors for polymer electrolyte fuel cells (PEFCs). The results showed the catalyst possessed superior performances for the reaction in the activity and the resistance to coke deposition even under a low H2O/CH4 molar ratio (S/C < 2) condition. (C) 2006 Elsevier B.V. All rights reserved.