We have investigated the expansion of MgB2 plasma plume produced by pulsed laser ablation of targets, obtained by pressing commercial powders with different compositional ratios. In order to evaluate the reactivity of the charged and neutral species, time- and space-resolved emission spectroscopy have been performed by using an optical multichannel analyser during the plasma plume expansion. The gaseous species have been collected on MgO(1 0 0) substrates which were positioned, by a heatable holder, in front of the target. The deposited thin films have also been electrically characterized. (C) 2002 Elsevier Science B.V. All rights reserved.