Silicon oxycarbide (SiOC) ceramics with highly adjustable properties and microstructures have many promising applications in batteries, catalysis, gas separation, and supercapacitors. In this study, additive structures on the nucleation and growth of SiO2 within SiOC ceramics are investigated by adding cyclic tetramethyl-tetravinylcyclotetrasiloxane (TMTVS) or caged octavinyl-polyhedral oligomeric silsesquioxane (POSS) to a base polysiloxane (PSO) precursor. The effects of the 2 additives on the polymer-to-ceramic transformation and the phase formation within the SiOC are discussed. POSS encourages SiO2 nucleation and leads to more SiO2 formation with significantly increased ceramic yield, which subsequently leads to higher specific surface of 1557m(2)/g with a larger pore size of similar to 1.8nm for the porous SiOC. High TMTVS content decreases both the specific surface area and pore volume of the resulting porous SiOCs. This study demonstrates a new approach of using Si-rich additive POSS to increase the SiOC yield while maintaining or even increasing the specific surface area.