  We study the full linear perturbations of a homogeneous and isotropic
spacetime in the Eddington-inspired Born-Infeld gravity. The stability of the
perturbations are analyzed in the Eddington regime. We find that, for positive
$\kappa$, the scalar modes are stable in the infinite wavelength limit ($k=0$)
but unstable for $k\neq0$. The vector modes are stable and the tensor mode is
unstable in the Eddington regime, independent of the wave vector $k$. However,
these modes are unstable and hence cause the instabilities for negative
$\kappa$.
