Schiff bases derived primarily from a variety of hetrocyclicring, were reported to possess abroad spectrum of pharma cological activities with various biological properties. A new heterocyclic Schiff bases ligand 4-(4-hydroxy -3,5 dimethoxy bezylidene amino)-1,5-dimethy -2-phenyl- 1H-pyrazol-3(2H)-one [L^1] derived from the condensation of 4- Amino antipyrine with 4-Hydoxy -3,5-dimethoxy benzaldehyde have been synthesized and characterized by FT-IR_( ,) Uv-Vis spectroscopy,〖〖^1〗H〗_9^ 〖^13〗C-NMRspectrum, mass spectrum, elemental microanalysis (C.H.N) and chloride content. Metal complexes with Co(II),Ni(II),Cu(II) and Pd(II) ions have been also synthesized and characterized by spectroscopic methods (FT-IR,Uv-Vis) spectroscopy, flam atomic absorption, molar conductivity measurements and magnetic susceptibility. This study indicates that the complex molar ratio (L:M) is (2:1). The complexes Co (II) and Ni(II) showed characteristics of octahedralgeometry with the (O,N) ligand coordinated in bidentate mode, while Cu(II) and Pd(II) showed square planer. The enzyme activity of the ligand and its metal complexes withAspartate amino transferase (AST)have also been studied. The study of enzyme activity indicates that the ligand and its metal complexes revealed different inhibition behaviours.