  In the paper, we give two new characterizations of separable inner
quasidiagonal C*-algebras. Base on these characterizations, we show that a
unital full free product of two inner quasidiagonal C*-algebras is inner
quasidiagonal again. As an application, we show that a unital full free product
of two inner quasidiagoanl C*-algebras with amalgmation over a full matrix
algebra is inner quasidiagonal. Meanwhile, we conclude that a unital full free
product of two AF algebras with amalgamation over a finite-dimensional
C*-algebra is inner quasidiagonal if there are faithful tracial states on each
of these two AF algebras such that the restrictions on the common subalgebra
agree.
