Let F(x) =∑∞n=1τs1,s2,...,sk (n)xn be the generating function for the number τs1,s2,...,sk (n) of spanning trees in the circulant graph Cn (s1,s2,...,sk).We show that F(x) is a rational function with integer coefficients satisfying the property F(x) =F(1/x).A similar result is also true for the circulant graphs C2n(s1,s2,...,sk,n) of odd valency.We illustrate the obtained results by a series of examples.