In　this　work,　an　Si/SiO2–ordered-mesoporous　carbon　(Si/SiO2–OMC)　nanocomposite　was　initially　fabricated　through　a　magnesiothermic　reduction　strategy　by　using　a　two-dimensional　bicontinuous　mesochannel　of　SiO2–OMC　as　a　precursor,　combined　with　an　NaOH　etching　process,　in　which　crystal　Si/amorphous　SiO2　nanoparticles　were　encapsulated　into　the　OMC　matrix.　Not　only　can　such　unique　porous　crystal　Si/amorphous　SiO2　nanoparticles　uniformly　dispersed　in　the　OMC　matrix　mitigate　the　volume　change　of　active　materials　during　the　cycling　process,　but　they　can　also　improve　electrical　conductivity　of　Si/SiO2　and　facilitate　the　Li+/Na+　diffusion.　When　applied　as　an　anode　for　lithium-ion　batteries　(LIBs),　the　Si/SiO2–OMC　composite　displayed　superior　reversible　capacity　(958　mA　h　g−1　at　0.2　A　g−1　after　100　cycles)　and　good　cycling　life　(retaining　a　capacity　of　459　mA　h　g−1　at　2　A　g−1　after　1000　cycles).　For　sodium-ion　batteries　(SIBs),　the　composite　maintained　a　high　capacity　of　423　mA　h　g−1　after　100　cycles　at　0.05　A　g−1　and　an　extremely　stable　reversible　capacity　of　190　mA　h　g−1　was　retained　even　after　500　cycles　at　1　A　g−1.　This　performance　is　one　of　the　best　long-term　cycling　properties　of　Si-based　SIB　anode　materials.　The　Si/SiO2–OMC　composites　exhibited　great　potential　as　an　alternative　material　for　both　lithium-　and　sodium-ion　battery　anodes.　©　2018　Wiley-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim