ObjectiveTo study the phenotype and functions of NK cells in mucosal associated lymphoid tissues (MALTs) from rhesus monkeys infected with SIV during acute phase. Methodsfour rhesus monkeys were inoculated with SIVmac239. Plasma viral load and CD4⁺/CD8⁺ ratio were detected at regular intervals. To obtain mucosal associated lymphoid tissues, ileum of animals was collected by operations at different times after inoculation. Then, mononuclear cells from this tissue were stained with antibodies, and detected with flow cytometry. ResultsCD56-CD16⁺ in MALTs were expanded in numbers and the degranulation functions were enhanced during acute phase of SIV infection. The ratio of DN NK cells were reduced but their functions showed unchangeable. The ratio of DP NK cells and CD56⁺CD16- NK cells increased slightly, but the immunoregulation functions were decreased. ConclusionsThe degranulation cytotoxicity potential of NK cells from gut associated lymphoid tissues (MALTs) from SIV infected rhesus monkey were enhanced during acute phase. This study plays an important role in the exploration of mucosal immunologic mechanism of SIV infection. 