In the present work, the spectroscopic and magnetic properties of heteronuclear Cu:Pr squarate are reported. Single crystals of [Pr2Cu(C4O4)4(H2O)16]·2H2O were obtained by reaction of squaric acid, praseodymium chloride and copper chloride in water solution according to the procedure described earlier. The crystals of title compound are isomorphic with [La2Cu(C4O4)4(H2O)16]·2H2O crystal, where squarate anions participate as bridging ligands between metal ions.The UV region of absorption spectra of the title compound is dominated by C–T band of Cu(II), f–d transition of Pr(III) and internal π–π*(A1g→Eu) and π–π*(A1g→Eg) ligand transitions. In visible and IR regions, t2g–eg of copper Cu(II) as well as 3H4→3PJ, 1D2, 1G4, 3FJ, 3H6 Pr(III) transitions at 293 and 4K were recorded. At low temperature splitting given by Jahn–Teller effect can be observed. Significant anisotropy of d–d transitions intensities confirms well the Jahn–Teller effect, too. Unexpectedly high intensity of 3H4→1G4 transition is probably due to the intensity borrowing from the Cu (II) d–d transition.The 3P0 and 1D2 emission of Pr(III) in the [Pr2Cu(C4O4)4(H2O)16]·2H2O crystals is quenched even at 77K. Whereas emission of appropriate polynuclear europium squarate was detected. The pathways of excited state quenching by eg levels of Cu(II), multhiphonon relaxation and concentration quenching can be considered in the system under studies. Magnetic susceptibility measurements were carried out in 300–1.7K temperature range and are discussed in relation to the structure.Effect of the polymeric structure on spectroscopic behaviour is presented. Selectivity of polymeric europium squarate in vitro test for different tumor cells is shown.