Abstract: Objective To reveal the change of aquaporin 1(AQP1) in malignant pleural tumor and their relationship. Methods Establish animal model of C57BL/6J mice with malignant pleural tumor, the tumor group was divided into three groups (T6，T8，T10). Based on the sixth, eighth, tenth day of injection, these mice were sacrifi ced and record the volume of the malignant pleural effusion, and determine the express of AQP1 and its mRNA in partial pleura using immunohistochemistry and Real-time PCR. Results 21 mice in MPE team appeared malignant pleural effusion in the right pleural cavity, MPE amount，level of VEGF and AQP1of the 3 groups was gradually increased. There was positive correlation between the level of AQP1 and VEGF in T6, T8, T10 group and the amount of MPE. Conclusion AQP1 participates in the formation of malignant pleural tumor, its level and the amount of pleural fl uid are positive correlation. Inhibiting the activition of AQP1 may be new ways to treat the malignant pleural tumor.