  Fermi Ball is a kind of nontopological soliton with fermions trapped in its
domain wall, and is suggested to arises from the spontaneous symmetry breaking
of the approximate $Z_2$ symmetry in the early universe. We find that the
neutral thin-wall Fermi Ball is stable in the limited region of the scalar
self-coupling constant $\lambda$ and the Yukawa coupling constant $G$. We find
that the Fermi Ball is stabilized due to the curvature effect of the domain
wall caused by the fermion sector. We also discuss whether such stable Fermi
Balls may contribute to the cold dark matter.
