The junction condition across a singular surface in general relativity, for
mulated by Israel, has double covariance. In this paper, a general perturba
tion scheme of the junction condition around an arbitrary background is giv
en in a doubly covariant way. After that, as an application of the general
scheme, we consider perturbation of the junction condition around a backgro
und with the symmetry of a (D - 2)-dimensional constant-curvature space, wh
ere D is the dimensionality of the spacetime. The perturbed junction condit
ion is written in terms of doubly gauge-invariant variables only. Since the
symmetric background includes cosmological solutions in the brane-world as
a special case, the doubly gauge-invariant junction condition can be used
as basic equations for perturbations in the brane-world cosmology.