In a support device (10,100) for aquarium accessories comprising a first fixing element (20) able to be applied on the inner surface of a wall (200) of an aquarium and a sustaining element (30) for an accessory of aquarium (150) able to be supported by said first fixing element (20), said first fixing element (20) has a concave cap (28) and said sustaining element (30) has a convex cap (32) able to be housed at least partially inside said concave cap (28). Furthermore, the support device (10,100) comprises a first magnetic or ferromagnetic element (40) in the form of a cap, the first fixing element (20) comprises a second magnetic or ferromagnetic element (26), and the convex cap (32) of the sustaining element (30) is interposed between the concave cap (28) of the first fixing element (20) and the first magnetic or ferromagnetic element (40) so that, due to magnetic attraction between the first magnetic or ferromagnetic element (40) and the second magnetic or ferromagnetic element (26), said sustaining element (30) is supported by the first fixing element (20) and, at the same time, it is rotationally movable.
