Periodic mesoporous organosilica (PMO) have been prepared from bis(triethoxysilyl)methane (BTM) and cetyltrimethylammonium chloride (C16TAC). A large range of synthesis conditions (pH, C16TAC/BTM ratio, post-treatment and concentration) were used to study their effects on the structure of the as-prepared meso-structured samples. The sample obtained with the optimised composition presents a 2D-hexagonal structure with a large surface area of about 950 m2/g. This material has been pyrolysed under Argon up to 1000 °C. Conversion into a silicon oxycarbide glass has been followed by X-ray diffraction. The organised structure can be retained until 800 °C. Further characterisations were performed by 29Si MAS NMR, 13C CP MAS NMR and N2 adsorption–desorption experiments to follow the structural changes occurring during the pyrolysis.