  In this article we consider Sturm-Liouville operator with $q\in
W_{1}^{2}[0,1]$ and Dirichlet boundary conditions. We prove that if the set
$\{(n\pi)^{2}:n\in \mathbb{N}\}$ is a subset of the spectrum of the
Sturm-Liouville operator with Dirichlet boundary conditions, then $q=0$ a.e.
