The structure of the title compound has been determined by three-dimensional X-ray diffraction methods. The crystals are monoclinic, space group P2₁/c with unit-cell dimensions a= 9.30(1), b= 18.94(2), c= 9.88(1)Å, β= 114.0(1)°, and Z= 4. The atomic positions have been determined by Patterson and Fourier methods and refined by full-matrix least squares to R 0.080 for 2 944 observed reflections. The molecule, which has a dimeric structure, lies on a crystallographic centre and the two praseodymium atoms are linked by four bridging trifluoroacetate groups. The metal atoms have eight-fold co-ordination in the form of a distorted square antiprism, the co-ordination sphere being completed by oxygen atoms from a unidentate trifluoroacetate group and three hydrate water molecules. The non-bonded oxygen atom of the unidentate group participates in both intra- and inter-molecular hydrogen bonding. Powder data point to the neodymium and europium analogues being isostructural with the present compound.