A sterilizer for water, with pump, particularly for aquariums, comprisingat least one element for irradiation of ultraviolet rays,and at least one duct portion for the passage of the water to be sterilized, which faces the irradiation element, the duct portion being permeable to ultraviolet radiation irradiated during use by the irradiation element,a pump for supplying water to the duct portion,a structure for hanging from a rim of a wall of a tank, which has a first supporting portion for the intake of the pump and a second supporting portion for the irradiation element and for the duct portion that faces it.
