  Gravitational couplings in bulk space-time include those terms which are
fixed by scattering amplitude of strings and ambiguous terms that are coming
from the field redefinitions. These field redefinitions can be fixed in the
bulk by ghost-free condition. In this paper we have revised the effective
gravitational couplings on D-branes by including the field redefinitions. We
find the gravitational effective action up to $\alpha'^2$-order.
