Dipeptidyl peptidase-IV (DPP-IV) is one of the mammalian serine proteases participated in the pathogenesis of diseases and DPP-IV inhibitors are now widely used as antidiabetic drugs. A new water soluble ternary copper (II) complex,-[Cu(PY-Phen) (phe) (H2O)]NO3 center dot H2O-(py-phen:pyrazino[2,3f][1,10]phenanthroline, phe:phenylalanine), has been synthesized and characterized by CHN analysis, ESI-MS, FTIR and single-crystal X-ray diffraction techniques. Fluorescence spectroscopy was researched to study the interaction between the complex and bovine serum albumin (BSA) and dipeptidyl peptidase-IV (DPP-IV). Chromophore of BSA and DPP-IV enzyme is changed upon addition of the complex. Additionally, the complex was shown to have promising inhibitory activities against DPP-IV with lower IC50 value. This study may provide new insights into the development of effective agents against diabetes. (C) 2018 Elsevier B.V. All rights reserved.