The title compound, potassium cadmium metaborate, crystallizes in a monoclinic cell, featuring infinite one-dimensional CdO(5) chains and trigonal planar B atoms in hexagonal B(3)O(6) metaborate ions. The trigonal bipyramidal CdO(5) chains and metaborate ions are interlinked to form a three-dimensional framework, creating channels running parallel to the [101] direction in which the potassium ions reside.