  We search for the tree-diagram dominated process $B^+ \rightarrow p
\overline{n} \pi^0$, using a data sample of $772 \times 10^6~B\overline B$
pairs collected at the $\Upsilon(4S)$ resonance with the Belle detector at the
KEKB asymmetric-energy $e^+ e^-$ collider. This is the first search with the
Belle detector for a decay mode including an anti-neutron. No significant
signal is observed and an $90\%$ credible upper limit on the branching fraction
is set at $6.1\times10^{-6}$.
