Er3+/Yb3+-codoped Y2O3 transparent ceramics were fabricated and characterized from the point of up-conversion luminescence. All the samples exhibit high transparency not only in the near-infrared band but also in the visible region. Under 980 nm excitation, the ceramics gave up-conversion luminescence with very intense green (525–560 nm), red (around 660 nm), and considerably intense blue (405 nm) emissions. It is worthwhile to point out that the blue emission, which only appears in halide, was clearly observed in Y2O3 transparent ceramic. The emission bands at 405, 525, 560, and 660 nm are attributed to the transitions from excited states 2H9/2, 2H11/2, 4S3/2, and 4F9/2 to the ground state 4I15/2 of Er3+ ions, respectively. For nearly all samples, the green emissions were stronger than red emissions, and the maximal emission intensities were obtained with (Er0.025Yb0.05Y0.938Zr0.01)2O3 ceramic (Yb/Er=20). The red and green luminescence result from a two-photon process, while the blue emission is due to a three-photon process.