SiBNC preceramic polymer was synthesized by reacting hexamethyldisilazane simultaneously with dichoromethylsilane and trichoroborane in one pot. The prepared precursors were investigated with respect to their chemical and phase composition, by means of FT-IR and XPS. The random arrangement of planar B-N units and Si-N bonds formed the desired polymer precursors with –Si-N-B- framework. The precursor was converted into multinary ceramics when heated above 800°C with the yields of 50.1wt%. Under N2, the obtained SiBNC ceramic remained amorphous up to 1700 °C and formed crystallization of Si3N4 at 1800°C. But under Ar atmosphere, the sample showed obvious crystallization of β-SiC and BNC2 at 1800°C.