The optical properties of a Ho3+/Yb3+ co-doped CaSc2O4 oxide material are investigated in detail. The spectral properties are described as a function of doping concentrations. The efficient Yb3+→Ho3+ energy transfer is observed. The transfer efficiency approaches 50 % before concentration quenching. The concentration-optimized sample exhibits a strong green emission accompanied with a weak red emission, showing perfect green monochromaticity. The results of the spectral distribution, power dependence, and lifetime measurements are presented. The green, red, and near-infrared (NIR) emissions around 545, 660, and 759 nm are assigned to the 5F4+5S2→5I8, 5F5→5I8, and 5F4+5S2→5I7 transitions of Ho3+, respectively. The detailed study reveals the upconversion luminescence mechanism involved in a novel Ho3+/Yb3+ co-doped CaSc2O4 oxide material.