Lanthanides (Ln) are a group of important elements usually found in nature as mixtures. Their separation is essential for technological applications but is made challenging by their subtly different properties. Here we report that crystallization of homochiral camphorate metalorganic frameworks (MOFs) is highly sensitive to ionic radii of lanthanides and can be used to selectively crystallize a lanthanide element into predesigned MOFs. Two series of camphorate MOFs were synthesized with acetate (Type 1 with early lanthanides LaDy) or formate (Type 2 with late lanthanides TbLu and Y) as the auxiliary ligand, respectively. The Ln coordination environment in each type exhibits selectivity for Ln(3+) of different sizes, which could form the basis for a new cost-effective method for Ln separation.