  We systematically calculate the isospin violating decay, $D_s^*\to D_s\pi^0$,
with the heavy meson chiral perturbation theory up to $\mathcal{O}(p^3)$
including the loop diagrams. The $\mathcal{O}(p^3)$ tree level amplitudes
contain four undetermined LECs. We use two strategies to estimate them. With
the nonanalytic dominance approximation, we get $\Gamma[D_s^\ast\to
D_s\pi^0]=(3.38\pm0.12)$ eV. With the naturalness assumption, we give a
possible range of the isospin violating decay width, $[1.11-6.88]$ eV. We find
that the contribution of the $\mathcal{O}(p^3)$ corrections might be
significant.
