Four new gallium(III)/indium(III), copper(II), selenium(IV) oxides, namely, Ga2Cu(SeO3)(4) (1), Ga2CuO(SeO3)(3) (2), and M2Cu3(SeO3)(6) (M=Ga 3, In 4), have been synthesized by hydrothermal or high-temperature solid-state reactions. The structure of Ga2Cu(SeO3)(4) (1) features a 2D layer of corner-sharing GaO6 and CuO6 octahedra with the SeO3 groups hanging on both sides of the 2D layer. Ga2CuO(SeO3)(3) (2) features a pillared layered structure in which the 1D Cu(SeO3)(3)(4-) chains act as the pillars between 2D layers formed by corner- and edge-sharing GaOn (n = 4, 5) polyhedra. Although the chemical compositions of M2Cu3(SeO3)(6) (M=Ga 3, In 4) are comparable, they belong to two different structural types. Ga2Cu3(SeO3)(6) (3) exhibits a pillared layered structure built by [Ga2Cu3(SeO3)(4)](4+) thick layers with Se(3)O-3(2-) groups as pillars. The structure of In2Cu3(SeO3)(6) (4) features a 3D network composed of [In-2(SeO3)(2)](2+) layers and [Cu-3(SeO3)(4)](2-) layers interconnected through Se-O-Cu and In-O-Cu bridges, exhibiting 8-MR helical tunnels along the a-axis. Results of magnetic property measurements indicate that there are considerable antiferromagnetic interactions between copper(II) centers in Ga2CuO(SeO3)(3) (2) and M2Cu3(SeO3)(6) (M = Ga 3, In 4). Interestingly, Ga2Cu3(SeO3)(6) (3) behaves as a weak ferromagnet below the critical temperature of T-c=15 K, Further magnetic studies indicate that the compound is a canted antiferromagnet with a large canting angle of about 7.1 degrees.