  We calculate the rate for $D_s^* \rightarrow D_s \pi^0$ decay using Chiral
Perturbation Theory. This isospin violating process results from $\pi^0$ -
$\eta$ mixing, and its amplitude is proportional to $(m_d -
m_u)/\bigl(m_s-(m_u+m_d)/2 \bigr)$. Experimental information on the branching
ratio for $D_s^* \rightarrow D_s \pi^0$ can provide insight into the pattern of
$SU(3)$ violation in radiative $D^*$ decays.
