The title compound, [Al(H(2)O)(6)][Cr(OH)(6)Mo(6)O(18)]·10H(2)O, hexa-aqua-aluminium hexa-hydroxidoocta-deca-oxido-molybdo-chromate(III) deca-hydrate, crystallizes isotypically with its gallium analogue [Ga(H(2)O)(6)][Cr(OH)(6)Mo(6)O(18)].10H(2)O. In the structure of the title compound, both the [Al(H(2)O)(6)](3+) cation and the Anderson-type [Cr(OH)(6)Mo(6)O(18)](3-) anion lie on centres of inversion. The anion is composed of seven edge-sharing octa-hedra, six of which are MoO(6) octa-hedra that are arranged hexa-gonally around the central Cr(OH)(6) octa-hedron. The anions are linked to each other by O-H⋯O hydrogen bonds into infinite chains along [100]. These chains are further connected with the [Al(H(2)O)(6)](3+) cations through O-H⋯O hydrogen bonds into sheets parallel to (01). O-H⋯O hydrogen bonds involving all the lattice water mol-ecules finally link the sheets into a three-dimensional network.