C-3N-4 crystals with the size of several micrometers have been synthesized from C-3N-4H-4 in the presence of nickel|based alloy or cobalt as catalyst under high pressure of 7 GPa and temperature of about 1400℃ for 10 min. Scanning electron microscopy, energy|disperse X|ray analysis, and X|ray diffraction were used to examine the grown crystals. The general rule on selecting the starting materials for synthesis of carbon nitride crystals at high pressures and high temperatures is suggested. C - 3N - 4 crystals with the size of several micrometers have been synthesized from C - 3N - 4H - 4 in the presence of nickel | based alloy or cobalt as catalyst under high pressure of 7 GPa and temperature of about 1400 ° C for 10 min. Scanning electron microscopy, energy | disperse X | ray analysis, and X | ray diffraction were used to examine the grown crystals. The general rule on selecting the starting materials for synthesis of carbon nitride crystals at high pressures and high temperatures is suggested.