To develop a vapor phase dimethyl carbonate synthesis process, the effects of reaction conditions and contaminants in feed materials on reaction performance have been investigated for CuCl₂/NaOH/activated carbon catalysts. A small spherical activated carbon particle with an average diameter of 60 μm was newly prepared. Optimal conditions for reaction temperature, pressure, contact time and reactant molar ratio were determined as follows: 393–423 K, 0.7–1.0 MPa, 0.1–0.3 kg-cat h m⁻³ and CH₃OH ∶ CO ∶ O₂ = 1 ∶ 3–4 ∶ 0.07–0.12, respectively. Among contaminants introduced, N₂, H₂, and CO₂ did not affect the catalyst performance. However, H₂O in the feed decreased the conversion of methanol and the selectivity of carbon monoxide to dimethyl carbonate. A fluidized bed reactor is preferable for the vapor phase reaction, considering the required temperature control and continual catalyst regeneration.