Structurally well-defined ordered mesoporous carbon (OMC)-supported uniform and specifically size-controlled Rh nanoparticle (NP) catalysts with low Rh content were prepared by three different methods (polyol, organometallic, and sonochemical) for higher alcohol synthesis from syngas. During the reaction, the size-confined Rh NPs in OMC were uniformly sintered, and the size of the aggregated Rh NPs was within the optimum metal size range for syngas-to-alcohol (STA) reaction. The catalytic reactions and TEM analyses clearly show that the uniform Rh NPs with a specific size in the OMC supports increase the STA catalytic performance by enhancing the CO insertion and reducing methane formation. Moreover, additional chain growth reactions for the synthesis of C3 and C4 alcohols could be produced by the use of uniform Rh nanoparticles on OMC supports.