A new hybrid organic–inorganic material with the structural formula unit [La(H2O)4(m-PO3C6H4COOH)(m-PO2(OH)C6H4COOH)(m-PO(OH)2C6H4COOH)]2 (or [La(H2O)4C21H18O15P3]2) has been synthesized under hydrothermal condition from La(NO3)3·6H2O and 3-phosphonobenzoic acid (m-PO(OH)2–C6H4–COOH) which is a rigid organic precursor possessing two types of functional groups: phosphonic acid and carboxylic acid. The two units of the produced hybrid are linked together by hydrogen bonds leading to a layered framework composing of by a repetition of inorganic and organic slices. The organic layers consist of dimeric units made of two meta-phosphono-benzoic acid linked together by hydrogen bonds involving their COOH groups. Two kinds of dimeric units are observed: PO3C6H4COOH⋯HOOCC6H4PO(OH)2, present 2 times in the structure, and PO2(OH)C6H4COOH⋯HOOCC6H4PO2(OH). The material crystallises in a monoclinic cell (C2/c (15) space group) with the following parameters: a = 42.515(4) Å, b = 7.4378(6) Å, c = 20.307(2) Å, β = 118.031(6)°, V = 5668.2(9) Å3, Z = 4, density = 1.908 g/cm3.