Abstract: Diamond crystals are grown by subjecting reaction materials of nondiamond carbon, a solvent metal, and diamond seeds to pressure and temperature conditions in the diamond-stable region. The reaction materials are in the form of a pair of a superimposed solvent metal plate and a nondiamond carbon plate or a pile made of a plurality of the pairs of the superimposed solvent metal plate and nondiamond carbon plate, and a plurality of the seeds are disposed on either one or each of the confronting surfaces of the pair of the superimposed solvent metal plate and nondiamond carbon plate. Alternatively, the reaction materials are in the form of a plate made of a mixture of the solvent metal and the nondiamond carbon or a pile made of a plurality of the mixture plates, and a plurality of the seeds are disposed on a surface of each plate. The seeds have a particle size of not larger than 50 .mu.