Seven new mixed-ligand vanadyl complexes, [V(IV)O(5-Br-SAA)(NN)] and [V(IV)O(2-OH-NAA)(NN)] (1-7) (5-Br-SAA for 5-bromosalicylidene anthranilic acid, 2-OH-NAA for 2-hydroxy-1-naphthaldehyde anthranilic acid and NN for N,N'-donor heterocyclic base, namely, 2,2'-bipyridine (bpy, 1 and 5), 1,10-phenanthroline (phen, 2 and 6), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, 3 and 7), dipyrido[3,2-a:2',3'-c]phenazine (dppz, 4)), were synthesized and characterized. X-ray crystal structure of [V(IV)O(5-Br-SAA)(phen)] revealed a distorted octahedral geometry with the Schiff base ligand coordinated in a tridentate ONO-fashion and the phenanthroline ligand in a bidentate fashion. Density-functional theory (DFT) calculations suggest a similar structure and the same coordination mode for all the other oxovanadium complexes synthesized. Biochemical assays demonstrate that the mixed-ligand oxovanadium(IV) complexes are potent inhibitors of protein tyrosine phosphatase 1B (PTP1B), with IC(50) values approximately 41-75 nM. Kinetics assays suggest that the complexes inhibit PTP1B in a competitive manner. Notably, they had moderate selectivity of PTP1B over T-cell protein tyrosine phosphatase (TCPTP) (about 2-fold) and good selectivity over Src homology phosphatase 1 (SHP-1) (about 4 approximately 7-fold). Thus, these mixed-ligand complexes represent a promising class of PTP1B inhibitors for future development as anti-diabetic agents.