  Pentaquark baryons $\Theta^{+}$ and $\Xi^{--}$ are studied in the dual
gravity theory of QCD in which simple mass formulae of pentaquarks are derived
in the Maldacena prototype model for supersymmetric QCD and a more realistic
model for ordinary QCD. In this approach it is possible to explain the
extremely narrow decay widths of pentaquarks. With the aim of constructing more
reliable mass formulae, a sketch is given on spin and the hyperfine interaction
in the string picture.
