To provide a new index of a change of intestinal bacterial flora.SOLUTION: There is provided a method for detecting a change of intestinal bacterial flora. In the method, the amount of at least one aquapolin(AQP) selected from a group comprising aquapolin3(AQP3), aquapolin7(AQP7) and aquapolin9(AQP9) existing in intestinal tract is measured, and a change of intestinal bacterial flora is detected by using the amount of the aquapolin as an index.SELECTED DRAWING: Figure 1
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