A new series of Cr(III), Mn(II), Fe(II), Co(II) and Ni(II) complexes of the 3-hydrazino benzoxazine-2-one (HBO) were prepared and characterized. The ligand behaves as a bis bidentate ONNN donor. The nature of bonding and the stereochemistry of the complexes have been deduced from elemental analyses, thermal, infrared, electronic spectra, magnetic susceptibility and conductivity measurements. An octahedral geometry was suggested for all the complexes. All the complexes show subnormal magnetic moments. The ligand, HBO, and its complexes were tested against Neurospora crassa, a non-pathogenic fungus. The Mn(II) and Co(II) complexes exhibited higher antifungal activities than the parent ligand.