Let \(\begin{aligned} \Delta _\lambda :=-\frac{\textrm{d}^2}{\textrm{d} x^2}+\frac{\lambda (\lambda -1)}{x^2}, \quad \lambda \ge 1, \end{aligned}\) be the Bessel operator on \(\mathbb {R}_+:=(0,\infty )\) , and consider its positive power \((\Delta _\lambda )^s\) ( \(0<s<1/2\) ), which is a nonlocal operator defined by the heat (or Poisson) semigroup. In this note, we investigate the asymptotic behavior of \((\Delta _\lambda )^s\) at \(s=0\) . A similar conclusion for the negative power is also considered.