  AdS/CFT predicts that the value of the on-shell action for type IIB
Supergravity (SUGRA) on $AdS_5 \times S^5$ background must be a non-zero number
completely determined from the boundary theory. We examine this statement
within Sen's formalism for type IIB SUGRA and find that consistency with
AdS/CFT requires us to add a specific boundary term to the action. We contrast
our resolution with two other resolutions recently proposed in the literature
in the context of different approaches to type IIB SUGRA. We explain how our
resolution presents a strong benchmark for the possible boundary term of the
complete spacetime action for type IIB superstring and how it may possibly lead
to a piece of evidence for the strongest form of AdS/CFT conjecture in $AdS_5
\times S^5$. We also comment on the fate of the on-shell action for general
self-dual $p$-form fields in Sen's formalism in any curved backgrounds.
