Objective To explore the value of fluorescence in situ hybridization (FISH) and multiplex RT-PCR in the detection of mixed lineage leukemia (MLL) gene rearrangement in acute leukemia (AL) patients. Methods Dual-color MLL probe, multiplex RT-PCR and R or G banding techniques were used to detect the MLL gene rearrangement in 189 cases of AL.Results MLL gene rearrangements were detected in 9 cases (5.03 ％) by FISH,and 16 cases (8.47 ％) by multiplex RT-PCR,including MLL/AF9,MLL/AF10,MLL/AF6, MLL/AF7, MLL/ELL, MLL/PTD. R or G banding techniques could find 11q23 in 5 out of 189 patients (2.65 ％). There was no statistic difference in the incidence of 6 common MLL gene rearrangements between ALL (73 cases) and AML patients (116 cases) (P ＞ 0.05).Conclusion Multiplex RT-PCR is a powerful technique in the detection of MLL gene rearrangement for tentatively diagnosed AL.It could not only confirm translocation detected by conventional cytogenetic method, but also detect MLL partial tandem duplication which could not been detected by cytogenetic examination or FISH. It plays an important role in guiding therapy and predicting prognosis for AL.