We have measured Raman spectra of diamond with nanometer size, called cluster diamond. The Raman bands assigned tosp2andsp3clusters have been observed at around 1600 and 1322 cm−1, respectively. This result suggests that the cluster diamond slightly contains thesp2cluster. The Raman band assigned tosp3cluster is found to shift by −10 cm−1, compared with that of bulk crystal and to be asymmetric with some tailing toward lower Raman frequency. The observed Raman spectrum agrees well with that calculated by a phonon confinement model. The crystallite size of the cluster diamond estimated from the phonon confinement model agrees approximately with that estimated from x‐ray measurement. Raman spectroscopy gives some information about the crystallite size of diamond particles with nanometer size. ©1995 American Institute of Physics.