Several possible flux materials have been investigated for preparing the superconducting YBa2Cu4O8 phase under 1 atm of oxygen. LiF was a promising flux and the YBa2Cu4O 8 phase was successfully obtained at 815°C with 0.5-1.0 wt.% LiF. Large amounts of LiF (>1.0wt.%) accelerated the formation of side products, i.e. BaCuO2 and Y2BaCuO5, instead of the superconducting phase. LiF was also used as a flux in the syntheses of the superconducting Y0.9Ca0.1Ba2Cu 4O8 and EuBa2Cu4O8 phases, and synthesis conditions for these compounds were optimized.