  We study the existence of least energy sign-changing solution for the
fractional equation $(-\Delta)^{s} u=|u|^{2_{s}^{*}-2}u+\lambda f(x,u)$ in a
smooth bounded domain $\Omega$ of $\mathbb{R}^{N},$ $u=0$ in
$\mathbb{R}^{N}\setminus \Omega$, where $s\in (0,1)$ and $2_{s}^{*}$ is the
fractional critical Sobolev exponent. The proof is based on constrained
minimization in a subset of Nehari manifold, containing all the possible
sign-changing solutions of the equation.
