The high temperature crystallization behavior of polytitanosilazane-derived amorphous SiTiN ceramics was investigated in a nitrogen atmosphere using XRD, Raman spectroscopy, TEM, SEM and BET. At 1400 °C, TiN is the first phase to nucleate in SiTiN ceramics forming nanocomposites with a homogeneous distribution of TiN nanocrystals within an amorphous Si3N4 matrix. Above 1400 °C, XRD indicates that the temperature at which Si3N4 crystallizes depends on the volume fraction of TiN present in nanocomposites. This is closely related to the chemistry of the polyorganosilazanes used to synthesize polytitanosilazanes. The use of perhydridopolysilazane, the most reactive polyorganosilazane, allows preparing TiN/Si3N4 nanocomposites with a remarkable stability of the amorphous matrix up to 1800 °C as mesoporous materials and powders. Dense monoliths crystallize earlier than the powder analogs because of the use of an ammonia pre-treatment before polymer warm-pressing.