Silicon nitride (Si3N4) powders were synthesized with silica sol, urea and carbon black by ammono sol2gel processing. Urea was dissolved in water and mixed homogeneously with silica sol. Ammonolysis of the aqueous solution could form a precursor, which was then mixed with carbon black and nitrided at 1300～1600℃under a flowing N2 atmosphere. The precursor and final powder were characterized by X-ray diffractometry, infrared spectroscopy and transmission electron microscopy. Results showed that Si3N4 powders with a size of 50～80nm and a content of more than 37% nitrogen can be obtained from the precursor annealed at 1500℃under a N2 flow of 3L/min for 2h. Effects of ammonolysis and synthesizing conditions on the final products were investigated.