Nanostructured and planar films of poly(p-xylylene) (PPX) are fabricated by an oblique angle polymerization method and coated with cobalt using electroless deposition. The catalytic activity of cobalt coated oil the nanostructured and planar PPX films is studied by measuring the rate of hydrogen evolution by the hydrolysis of alkaline-stabilized sodium borohydride (NaBH4) solution. The hydrogen release rate data show an asymptotic increase for the structured PPX film as a function of the electroless bath time, but the planar PPX films show a lower catalytic activity due to the inefficiency of cobalt deposition. The hydrogen release rate of the cobalt-coated nanostructured PPX film shows a rate between 2000 and 4250 mL(g min)(-1) (i.e., rate of hydrogen gas per cobalt mass at room temperature and pressure), which is comparable to the values obtained on platinum, and ruthenium systems. (C) 2008 Elsevier B.V. All rights reserved.