Using Czochralski (CZ) pulling method, an Er3+/Yb 3+-codoped NaY(WO4)2 crystal was prepared. Absorption spectra, emission spectra and excitation spectra of this crystal were measured at room temperature. Some optical parameters, such as intensity parameters, spontaneous emission probabilities and lifetimes, were calculated from absorption spectra with Judd-Ofelt (J-O) theory. Upconversion luminescence excited by a 970 nm diode laser was studied. In this crystal, green upconversion luminescence is particularly intensive. Energy transfer mechanisms that play an important role in upconversion processes were analyzed. Two cross-relaxation processes: 4G11/2 + 4I9/2 → 2H11/2 (or 4S3/2) + 2H11/2 (or 4S3/2), and 4G11/2 + 4I15/2 → 2H11/2 (or 4S3/2) + 2I13/2, which contribute to the intensive green luminescence under 378 nm excitation, were put forward. Background energy transfer 4G11/2(Er3+) + 2F 7/2(Yb3+) → 4F9/2(Er 3+) + 2F5/2(Yb3+) was also demonstrated. © 2005 Elsevier B.V. All rights reserved.