The interactions between four high bioactive diperoxovanadate complexesKn[OV(O2)2L]·mH2O (n = 1 ～3, m = 1～5, L = oxalate (abbr. oxa), picolinate (abbr. pic), bipyridine (abbr. bipy) and 1,10-phenanthroline (abbr. phen); their corresponding complexes abbreviated as bpV(oxa), bpV(pic), bpV(bipy) and bpV(phen), respectively) and imidazole (abbr. imi) in solution were studied by several NMR techniques: multinuclear (1H, 13C and 51V) and variable temperature 51V NMR. Competitive coordination interactions were observed and the order of the interaction strength of the four complexes with imidazole is as follows: bpV(oxa) ＞ bpV(pic) ＞ bpV(bipy) ＞bpV(phen), which is deeply affected by the identity of the ligands and has the same order as their inhibition effect toward bovine heart phosphotyrosyl protein phosphatase. The species [OV(O2)2(imi)]- was formedin all cases. Both of the NMR data and equilibrium constants of the interaction systems were reported. The experimental results indicate that the species of bpV(oxa)and [OV(O2)2(imi)]- are six-coordinated, while bpV(pic), bpV(bipy) and bpV(phen) are sevencoordinated in solution. ESI-MS results support the conclusions obtained by NMR.