We describe the synthesis, Langmuir-Blodgett (LB) film formation, and photo-oxidation of an organic-inorganic hybrid block copolymer consisting of N-dodecyl 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 air-water interface was confirmed for p(DDA/SQ26)-b-pDDA. The p(DDA/SQ26)-b-pDDA monolayer was deposited onto solid substrates with a monolayer thickness of 2.3 nm. The photo-oxidized SiO2 nanofilm revealed its porous structure, which reflects phase-separated structures of p(DDA/SQ26)-b-pDDA, 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 organic-inorganic hybrid block copolymer LB film is promising for manipulating pore formations of inorganic oxide nanofilms.