The role of the WW domain-containing oxidoreductase (WWOX) gene in multiple types of solid human cancers has been documented extensively thus far. Recently, we investigated the in vitro effects of WWOX overexpression and observed marked growth arrest in human leukemia cells; however, the clinical characterization of WWOX in leukemia remains poorly investigated. The present study evaluated the WWOX expression profiles of 182 patients with leukemia of different types and 5 leukemic cell lines, using reverse transcription-polymerase chain reaction and immunofluorescence analysis. The results found that WWOX mRNA and WWOX protein expression was significantly reduced or absent in the leukemia cases and cell lines compared with paired controls. The WWOX-positive rate was also lower in the leukemia cases compared with the rate of the normal controls. Notably, the WWOX level was reduced in newly diagnosed and relapsed cases, or in chronic myelogenous leukemia in the blastic phase, yet elevated in remission samples. Moreover, WWOX-negative cases exhibited WWOX expression restoration following induced remission. These findings suggest that WWOX may contribute to the occurrence and development of leukemia, and that it has potential to be a good biomarker or predictor for leukemia therapy.