  In the present paper, we briefly review recent studies of second-order
gravitational perturbations in braneworld models. After we consider the
possibility of pathological behavior of gravity at higher orders of
perturbation, second-order perturbations are discussed in Randall-Sundrum
braneworld models. Because the mass spectra in these braneworld models are
different, we analyze them using different approaches. In the respective
models, it is discussed that 4D Einstein gravity is approximately recovered at
level of second-order perturbation, although there are some exceptional cases
in the two-brane model.
