Liquid-phase methanol synthesis was investigated using copper-based ultrafine particle (UFP) catalysts. Cu-Zn UFP catalyst was active for methanol synthesis, although the activity decreased with time-on-stream. Cu-V UFP catalyst was stable against deactivation and showed the highest methanol productivity of the catalysts tested. The space time yield of methanol on this catalyst was about 3.5 times as large as that of a co-precipitated Cu-Zn catalyst. The selectivity of the Cu-V UFP catalyst for methanol was low, as compared to that of the co-precipitated Cu-Zn catalyst, due to the formation of methane. The addition of carbon dioxide in the feed gas was effective in suppressing the formation of methane.