The structures of benzylhydroxamamide (BHam, LH) conformers, deprotonated (L - ) species and their technetium complexes have been obtained by geometry optimizations using Hatree-Fock at different basis sets and density functional theory calculations at B3LYP/6-31G(d) level of theory. Two hydroxyimino and ten hydroxyamino conformers of BHam have been found. Conformational pathways of all stable BHam conformers and their oxo-Tc(V) complexes have been investigated. The tautomerization between hydroxyimino and hydroxyamino tautomers is an endothermic reaction, with ΔH o =7.38kcal/mol and its equilibrium constant logK=-5.70, at 298.15 K. The stabilization energies of oxo-Tc(V) complexes existing as [(LH) 2 TcO] + 3 , [L 2 TcO] + of C 2 and [L 2 TcO] + of C 2 v conformers have been determined at HF/3-21G level of theory. The optimized geometry of hydroxyimino tautomer is the most stable species and shows good agreement with X-ray crystallographic data.