Supercritical water (SCW) has various physicochemical properties tunable with its temperature and pressure conditions. In recent years, SCW has been used as a new reaction medium for the preparation of carbon. Particularly, the presence of a radical initiator in SCW has provided carbon particles even at the low temperature of 400°C. Furthermore, the selection of adequate starting materials in the corresponding system enables the formation of carbon-metal oxide composites. Here we review research on the application of SCW media to carbon formation.