RbTb(SO6)2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Rb is bonded in a 8-coordinate geometry to eight O atoms. There are a spread of Rb–O bond distances ranging from 2.90–3.50 Å. Tb is bonded in a 8-coordinate geometry to eight O atoms. There are a spread of Tb–O bond distances ranging from 2.29–2.67 Å. There are two inequivalent S sites. In the first S site, S is bonded in a tetrahedral geometry to four O atoms. There are a spread of S–O bond distances ranging from 1.45–1.53 Å. In the second S site, S is bonded in a tetrahedral geometry to four O atoms. There are a spread of S–O bond distances ranging from 1.43–1.54 Å. There are twelve inequivalent O sites. In the first O site, O is bonded in a water-like geometry to one Rb and one O atom. The O–O bond length is 1.23 Å. In the second O site, O is bonded in a single-bond geometry to one Rb and one S atom. In the third O site, O is bonded in a 1-coordinate geometry to one Rb, one Tb, and one S atom. In the fourth O site, O is bonded in a bent 150 degrees geometry to one Tb and one S atom. In the fifth O site, O is bonded in a bent 150 degrees geometry to one Tb and one S atom. In the sixth O site, O is bonded in a bent 120 degrees geometry to one Rb and one Tb atom. In the seventh O site, O is bonded in a 4-coordinate geometry to two equivalent Rb, one Tb, and one S atom. In the eighth O site, O is bonded in a water-like geometry to one Tb and one S atom. In the ninth O site, O is bonded in a single-bond geometry to one S atom. In the tenth O site, O is bonded in a distorted single-bond geometry to two equivalent Rb, one Tb, and one S atom. In the eleventh O site, O is bonded in a distorted single-bond geometry to one O atom. In the twelfth O site, O is bonded in a bent 150 degrees geometry to one Tb and one O atom. The O–O bond length is 1.97 Å.