Hydrogen is the preferred fuel for getting high performance from polymer electrolyte fuel cell (PEMFC). On-board hydrogen production is a promising alternative for fueling micro-PEMFC due to unavailability of good quality hydrogen storage material with high volume/weight percentage of hydrogen, but the minimization of the hydrogen generator along with controlling hydrogen flow rate remain a challenge. The main aim of the present research work is to develop a portable fuel processor to generate hydrogen instantly in a controlled way from water. Hydrogen is produced from water in an auto-electrolytic process after connecting the magnesium (Mg) and stainless steel (S.S.) plates as the anode and cathode respectively, and the plates are immersed in an electrolytic solution. Different parameters, e.g. effect of various concentrations of the electrolytic solution, varying gap between the electrodes, and various combinations of electrode connections for multiple electrodes on the rate of hydrogen production were studied. The controlled circuit was developed for controlling hydrogen flow rate with two types of control systems, varying resistance and on/off switch, being tested. The fuel processor having 95 x 10(-6) m(3) inner volume can be operated for about 3 h with the hydrogen flow rate of 40 x 10(-6) m(3)/min. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.