Highly ordered mesoporous silicon carbide ceramics have been successfully synthesized with yields higher than 75% via a one-step nanocasting process using commercial polycarbosilane (PCS) as a precursor and mesoporous silica as hard templates. Mesoporous SiC nanowires in two-dimensional (2D) hexagonal arrays (p6m) can be easily replicated from a mesoporous silica SBA-15 template. Small-angle X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images show that the SiC nanowires have long-range regularity over large areas because of the interwire pillar connections. A three-dimensional (3D) bicontinuous cubic mesoporous SiC structure (Ja3d) can be fabricated using mesoporous silica KIT-6 as the mother template. The structure shows higher thermal stability than the 2D hexagonal mesoporous SiC, mostly because of the 3D network connections. The major constituent of the products is SiC, with 12% excess carbon and 14% oxygen measured by elemental analysis. The obtained mesoporous SiC ceramics are amorphous below 1200 degrees C and are mainly composed of randomly oriented beta-SiC crystallites after treatment at 1400 degrees C. N-2-sorption isotherms reveal that these ordered mesoporous SiC ceramics have high Brunauer-Emmett-Teller (BET) specific surface areas (up to 720 m(2) g(-1)), large pore volumes (similar to 0.8 cm(3) g(-1)), and narrow pore-size distributions (mean values of 2.0-3.7 nm), even upon calcination at temperatures as high as 1400 degrees C. The rough Surface and high order of the nanowire arrays result from the strong interconnections of the SiC products and are the main reasons for such high surface areas. XRD, N-2-sorption, and TEM measurements show that the mesoporous SiC ceramics have ultrahigh stability even after re-treatment at 1400 degrees C under a N-2 atmosphere. Compared with 2D hexagonal SiC nanowire arrays, 3D cubic mesoporous SiC Shows superior thermal stability, as well as higher surface areas (590 m(2) g(-1)) and larger pore volumes (similar to 0.71 cm(3) g(-1)).