The red upconversion (UC) emission of Eu3+ ions in Lu2O3: Yb3+/Eu3+ powders was successfully enhanced by tridoping Ho3+ ions in the matrix, which is due to the bridging function of Ho3+ ions. The experiment data manifest that, in Yb3+/Eu3+/Ho3+ tridoped system, the Ho3+ ions are first populated to the green emitting level 5F4/5S2 through the energy transfer (ET) processes from the excited Yb3+ ions. Subsequently, the Ho3+ ions at 5F4/5S2 level can transfer their energy to the Eu3+ ions at the ground state, resulting in the population of Eu3+5D0 level. With the assistance of the bridging function of Ho3+ ion, this ET process is more efficient than the cooperative sensitization process between Yb3+ ion and Eu3+ ion. Compared with Lu2O3: 5 mol % Yb3+/1 mol % Eu3+, the UC intensity of Eu3+5D0→7F2 transition in Lu2O3: 5 mol % Yb3+/1 mol % Eu3+/0.5 mol % Ho3+ is increased by a factor of 8.