Silicon carbide (SiC) has become a very important material for many high-performance applications as a result of its exceptional material properties. The emergence of size-dependent properties in SiC nanocrystals (SiC-NCs), together with the increased surface area intrinsic to nanocrystals, has led to a variety of new possible applications, including optoelectronics and hybrid materials. Here we report the straightforward preparation of size-controlled oxide-embedded and freestanding SiC-NCs from the reductive thermal processing of compositionally controlled phenylsiloxane polymers. Compositional tuning of the polymers is achieved by varying the relative amounts of phenyl trichlorosilane (C6H5SiCl3) and silicon tetrachloride (SiCl4) during hydrolysis and cocondensation. Thermal processing of the resulting compositionally controlled condensation copolymers yields oxide-embedded SiC-NCs whose average diameter is dependent on the relative C6H5SiCl3 concentration in the initial precursor mixture. A liberation procedure for preparing size-controlled freestanding SiC-NCs that involves oxidation of matrix carbon and subsequent chemical etching of the matrix is also presented.