Abstract: 100-textured diamond films were deposited on alumina ceramic substrates by microwave plasma chemical vapor deposition (MPCVD). The effects of the deposition condition on texture were also investigated based on the results of scanning electron microscopies (SEM), X-ray diffraction spectra (XRD) and Raman scattering spectra. Because of its higher ionization energy, a small portion of helium was introduced into the general post-growth etching process to improve the etching efficiency. According to the results from the etching experiments performed on 100 and 111-textured diamond films respectively, the selective etching of non-100-oriented grains by hydrogen plasma with helium addition is observed and it could be used to shorten the etching time and improve the 1O0 texture of the diamond films.