The recombination coefficient for the reaction O + O --> O-2 on a polycrystalline niobium surface was measured at various experimental conditions. The source of O atoms was a low pressure weakly ionized highly dissociated oxygen plasma created in a RF discharge. The electron temperature in plasma was about 5 eV and the density of positive ions between 5 and 10 x 10(15) m(-3). The density of neutral oxygen atoms was measured in the afterglow with a nickel catalytic probe and was between 2.5 and 7 x 10(21) m(-3). The recombination coefficient was measured at different temperature between 420 and 620 K, and was found to be a constant within the limits of the experimental error at the value of 0.09 +/- 0.018. (C) 2003 Elsevier Science B.V. All rights reserved.