We describe the synthesis, LangmuirBlodgett (LB) film formation, and photo-oxidation of an organic-inorganic hybrid block copolymer consisting of Ndodecyl acrylamide (DDA) and silsesquioxane (SQ) comonomers [p(DDA/SQ26)-b-pDDA].The copolymer was synthesized by reversible addition fragmentation chain transfer polymerization of DDA and SQ. Higher monolayer stability at the airwater interface was confirmed for p(DDA/SQ26)-fbpDDA. The p(DDA/SQ26)b--pDDA monolayer was deposited onto solid substrates with a monolayer thickness of 2.3 nm. The photo-oxidized Si0O nanofilm revealed its porous structure, which reflects phase-separated structures of p(DDA/SQ26)-fbpDDA, as confirmed using atomic force microscopy, quartz crystal microbalance, and cyclic voltammetry measurements. These results demonstrate that this preparation method using photo-oxidation of the organicinorganic hybrid block copolymer LB film is promising for manipulating pore formations of inorganic oxide nanofilms.