In our investigation, we fabricated cuprous oxide/activated carbon fibers (Cu2O/ACF) by depositing Cu2O cubes in situ on the ACF. A possible growth mechanism of Cu2O supported on the ACF is proposed. The adsorption and photocatalytic properties of Cu2O/ACF were studied with Methyl orange (MO) as the target pollutant. The results show that the Cu2O/ACF possessed more excellent adsorption properties than ACF, the adsorption efficiency reached 89.4% after 24 h. The synergetic effect between the Cu2O microstructure and ACF makes the Cu2O/ACF possess good photodegradation properties, the photocatalytic efficiency reached 86.1% after 6 h.