  We investigate cosmic-ray antiprotons emitted from the galactic primordial
black holes in the Randall-Sundrum type-2 braneworld. The recent results of the
BESS antiproton observation implies the existence of exotic primary sub-GeV
antiprotons, one of whose most probable origin is PBHs in Our Galaxy. We show
that the magnitude of antiproton flux from PBHs in the RS braneworld is
proportional to negative power of the AdS radius, and immediately find that a
large extra-dimension can relax upper-limits on the abundance of the Galactic
PBHs. If actually there are more PBHs than the known upper-limit obtained in
the pure 4D case, they set a lower bound on the size of the extra dimension
above at least 10^{20} times 4D Planck-length to avoid inconsistency. On
completion of the numerical studies, we show that these constraints on the AdS
radius is comparable to those obtained from the diffuse photon background by
some of the authors in the previous paper. Moreover, in the low accretion-rate
case, only antiprotons can constrain the braneworld. We show that we will
detect signatures of the braneworld as a difference between the flux of the
antiprotons predicted in 4D and 5D by future observations in sub-GeV region
with a few percent precision.
