In this paper, we report a novel route to the synthesis of high-quality, large-pore periodic mesoporous organosilicas (PMOs) using triblock copolymer P123 as a template. The novelty lies in that highly ordered PMOs can only be synthesized at a limited range of low acid concentrations, which differs from traditional approach to the synthesis of similar materials including large-pore periodic mesoporous silicas (PMSs). The role that acid plays in the synthesis of high-quality PMOs and PMSs was critically examined, compared, and interpreted.