Flash sintering (FS) is a newly emerging technology that can be applied to the synthesis and preparation of ceramics and ceramic matrix composites (CMCs). The electric field-assisted FS process is implemented through rapidly heating graphite papers/felts to high temperatures (up to 3000 °C) in inert atmosphere. The main technological advantage of the FS is that the green body enables sudden consolidation and densification in few seconds, in terms of low cost and energy efficiency. Here, we investigated the FS behavior of polymer-derived silicon oxycarbide (SiOC). The preceramic polymer of SiOC was first pyrolyzed at 1100 °C in Ar in order to remove the gaseous substances in the polymer molecular chain. Subsequently, the small amount of the preceramic polymer (1, 2, and 3 wt.%) as binder was added into the pyrolyzed powder to shape the SiOC bulk. Finally, the green body was heated to ~1700 °C in 30 seconds under Ar. The research focuses on the mass loss, linear shrinkage, and densification of the resulting ceramics. Also, the phase composition and microstructure of SiOC were characterized. The results are helpful to understand the FS mechanism of polymer-derived ceramics (PDCs), and provide more possibilities for developing ceramic components with relatively complex geometry.