Deuterium recombination coefficients on pure tungsten have been experimentally studied. Tungsten samples were continuously exposed to deuterium RF plasma and, simultaneously, deuterium surface densities and bulk concentrations were observed by using a nuclear reaction analysis. From consideration of deuterium particle balance between surface and bulk, the recombination coefficient on the plasma-exposed surface, k(u) = 4.5 x 10(-25) exp(-0.78 eV/kT) m(4) s(-1), was obtained at temperature range of 426-654 K. A potential energy diagram for hydrogen (deuterium) near tungsten surface was proposed based on the results. The diagram indicates that tungsten hardly absorbs hydrogen molecules and hydrogen atoms once entering into tungsten are not easily desorbed due to a high potential barrier between surface and vacuum. (C) 2010 Elsevier B.V. All rights reserved.