  We have successfully prepared an optically trapped ultracold mixture of
$^{23}$Na and $^{87}$Rb atoms and studied their interspecies Feshbach
resonances. Using two different spin combinations, several s-wave and p-wave
resonances are identified by observing a high inelastic loss and a temperature
rising for both species near resonant magnetic field values. The two s-wave
resonances observed below 500 G between atoms in the lowest energy level are
possible candidates for Feshbach molecule association. Our results are well
characterized by a coupled-channel model and are used refining the ground state
interaction potentials between $^{23}$Na and $^{87}$Rb. This work opens up the
prospect for preparing ultracold ensembles of ground-state bosonic NaRb
molecules which are chemically stable and can provide strong dipolar
interactions.
