||In the electrochemical CO2 reduction reaction (CO2RR), the extrinsic properties and the operating conditions are very important along with the intrinsic properties of the electrocatalyst. Herein, we report guidelines for selecting carbon support materials suitable for CO2RR. Ag nanoparticle-composited carbon nanocage (denoted as Ag/CNC) showcased a uniformly dispersed morphology with Ag nanoparticles and sufficient hydrophobicity after the reaction to prevent flooding, which is known to inhibit the mass transfer of CO2. Furthermore, the CNCs possessed small amounts of carbon defects; this suppressed the catalytic activity for the hydrogen evolution reaction (HER). Our study suggests that the support material for CO2RR should be considered not only on the basis of morphology of carbon, uniform dispersion of Ag nanoparticles, and hydrophobicity of the electrode, but also factors influencing the HER, such as carbon defects.