In this work, we perform a comparison study of hydrogen incorporation among nano-, micro-, and polycrystalline diamond films grown by microwave plasma assisted chemical vapor deposition (CVD). Hydrogen incorporation was assessed by means of Fourier-transforin infrared (FTIR) spectroscopy. Scanning electron micrographs show that from polycrystalline through microcrystalline to nanocrystalline diamond film, not only the grain sizes decrease but also the crystalline quality decreases in tenus of secondary nucleation or structural defects. Raman spectra confirms this observation by showing the broadening of the diamond Raman peak around 1332 cm(-1) and the increasing in intensity Of sp(2) bonded carbon band around 1500 cm(-1). Accompanying with the change in morphology and quality, the corresponding CH stretching bands in their FTIR spectra rise rapidly in intensity with shape change as well, indicating from polycrystalline to nanocrystalline diamond film, hydrogen impurity content increases drastically with decrease of grain size. The results are discussed and compared to those in the literature. The huge increase of hydrogen content in nanocrystalline diamond film suggests that hydrogen incorporated not only into grain boundaries but also into other structural defects of CVD diamond. (c) 2006 Elsevier B.V All rights reserved.