The boron modified poly(vinyl)silazane polymer precursor with the chemical composition (B[C2H4Si(CH3)NH]3)n was milled and sieved. The polymer particles from different size fractions were compacted using a graphite die in a uni-axial warm pressing machine at a pressure of 48 MPa and in the temperature range 250°C to 330°C. The green bodies were pyrolysed in an argon atmosphere at a temperature of 1300°C when the organic polymer converts into an inorganic amorphous Si-B-C-N ceramic. These amorphous ceramics were annealed under various conditions of temperature, nitrogen overpressure and holding time in order to crystallize them and to produce nano-crystalline microstructures. Compression creep experiments were carried out in atmospheric ambience at loads varying from 5 – 100 MPa and in the temperature range 1350°C – 1500°C to investigate the high temperature deformation behaviour of the crystalline material. The interest is to understand the mechanisms of deformation in these nanocrystalline Si-B-C-N ceramics at elevated temperatures and to compare the results with that of amorphous ceramics. The investigation also includes the determination of viscosity of the material at high temperatures.