Let A be a central Galois algebra with Galois group G which are inner automorphisms induced by elements in A

and C the center of A. Then a one-to-one correspondence between the following sets is given: (1){T|T is a separable subalgebra of A over C such that the commutant of T in A is a projective group algebra}

and (2) {H|H is a subgroup of G}. Also

some properties of projective group subalgebras and their commutants are proved.