High purity molybdenum was implanted by C ion in a metal vapour vacuum arc (MEVVA) implanter. The influence of implantation parameters was studied by varying ion fluence and ion current density. The samples were implanted by 45 keV C ion with fluences from 1 x 10(15) to 1 x 10(18) ions/cm(2), respectively. The as-implanted samples were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and nanoindenter. Different morphologies were observed on the surfaces of the as-implanted samples due to irradiation damage, and clearly related to implantation parameters. XRD spectra confirm formation of beta-Mo2C with ion fluences equal to or larger than 1 x 10(16) ions/cm(2), and formation of alpha-Mo2C with ion fluence of 1 x 10(18) ions/cm(2). The maximum nanohardness and maximum modulus of the as-implanted samples increased gradually with increasing ion fluence, and reached the corresponding maximum values with ion fluence of 1 x 10(18) ions/cm(2). The experimental results suggest that the structure and properties of the as-implanted Mo samples exhibited strong dependence on implantation parameters. (C) 2003 Elsevier B.V. All rights reserved.