  We search for the strange pentaquark $\Theta^+$ using kaon interactions in
the material of the Belle detector. No signal is observed in the $p K_S$ final
state, while in the $p K^-$ final state we observe $\sim 1.6 \cdot 10^4$
$\Lambda(1520) \to p K^-$ decays. We set an upper limit on the ratio of
$\Theta^+$ to $\Lambda(1520)$ yields $\sigma(\Theta^+) / \sigma(\Lambda(1520))
< 2%$ at 90% CL assuming that the $\Theta^+$ is narrow. We also report on
searches for strange and charmed pentaquarks in B meson decays. These results
are obtained from a 155$fb^{-1}$ data sample collected with the Belle detector
near the $\Upsilon(4S)$ resonance, at the KEKB asymmetric energy $e^+ e^-$
collider.
