The synthesis, X-ray structure, spectroscopic and magnetic properties of a zig-zag formato-bridged chain complex with the formula [Cu(dpyam)(μ-O 2CH)(OH2)]n(NO3)n (1) (in which dpyam = di-2-pyridylamine) is described. The geometry of the copper(II) ion is distorted square pyramidal with a basal plane consisting of two nitrogen atoms of the dpyam ligand (Cu-N distances 1.987(3) and 2.010(3) Å) and two oxygen atoms of two different formato ligands (Cu-O distances 1.974(2) and 1.975(2) Å). A coordinated water molecule occupies the axial position at a distance of 2.222(3) Å. The copper atoms are bridged unsymmetrically by a formato anion in a syn-anti arrangement, resulting in a polymeric zig-zag chain structure. The magnetic susceptibility measurements (5-280 K) agree with a very weak ferromagnetic chain interaction between the Cu centres with a J value of 0.75 cm-1.