The crystal structure of the title compound, Ce[B(4)O(6)(OH)(2)]Cl, is built from polyborate sheets parallel to the (001) plane. These sheets stack along the [001] direction and are linked by Ce atoms exhibiting an CeO(8)Cl(2) coordination sphere. O-H⋯O and O-H⋯Cl hydrogen bonds additionally stabilize the structural set-up. The polyborate sheet is made up of zigzag borate chains running along the [[Formula: see text]10] direction. These zigzag chains are inter-connected by shared O-vertices, resulting in a two-dimensional layer with nine-membered rings. All B and O atoms (except for the terminal OH atoms) lie in the nearly planar sheets of polyborates, leading to their isotropic atomic displacement parameters being significantly smaller than usual. This may be attributed to the fact that the atomic displacement parameters correlate not only with their atomic masses but with their coordination environments also.