The influences of various metal (Co, Ni, Cu, Ag and Mn) and carbon precursors (methane and graphite) on diamond synthesis in hot filament chemical vapor deposition (HFCVD) and microwave plasma chemical vapor deposition (MPCVD) were investigated. Diamond film is formed uniformly from 1% CH4/H-2, while blocks of diamond films and particles are produced from graphite/H-2. The promotion effects of the metals on diamond growth were observed by the variations of particle size in SEM and diamond peak intensity in XRD. Those containing Co or Ni powders exhibit the highest diamond growth rate from 1% CH4/H-2, but the catalytic effects of the metals are not as significant as proposed in some of the literature. Graphite, instead of methane, can be used for diamond synthesis, but with lower growth rate and nucleation density. It is concluded that the diamond growth mechanism for the samples containing metal, using either methane or graphite as a carbon precursor, similar to that of low-pressure CVD diamond.