Hydrogen was produced via electrolysis of aqueous formic acid solutions, and the effects of the concentrations of formic acid and NaOH on the electrolytic voltage were systematically investigated. The voltage is found to be related to the actual formic acid concentration. When the actual formic acid concentration is higher than 0.8 x 10(-9) M, the initial electrolytic voltage can be as low as 0.30 V, which is much lower than the open circuit voltage in a proton exchange membrane fuel cell. The electrolytic voltage increases with the increase of the current density. Specifically at 1.0 M NaOH and 4.0 M HCOOH, the steady voltage value increases from 0.62 to 0.70 V as the current density increases from 1.0 to 6.0 mA/cm(2). At 3.0 M HCOOH and 2.5 M NaOH, the hydrogen production rate is 53 mu mol/h under 8.0 mA/cm(2), which is promising for practical industrial-scale hydrogen production. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.