The ‘4+1’ mixed ligand strategy enables radiolabeling of biomolecules with ^99mTc at low ligand concentration without affecting it’s in vivo biological activity. The ‘4+1’ mixed-ligand complexes consist of central Tc(III) metal atom coordinated to a tetradentate tripodal chelator 2,2’,2’’-nitrilotriethanethiol (NS₃) and a monodentate isocyanide group tethered to a biomolecule. The present work describes the use of ‘4+1’ mixed ligand strategy to design radiopharmaceuticals for the detection of tissue hypoxia in vivo. Isocyanide derivatives of two nitroimidazoles, viz. 2-nitroimidazole (2NimNC) and metronidazole (MetNC), were synthesized and radiolabeled with ^99mTc using ‘4+1’ mixed ligand approach. The complexes [^99mTc(NS₃)(2NimNC)] and ^[99mTc(NS₃)(MetNC)] could be prepared in excellent yield (>90%). The structure of ^99mTc-complexes prepared at the no-carrier-added (nca) level was corroborated by spectroscopic analysis of corresponding rhenium analogues at the macroscopic level. Preliminary biological evaluation of the two nitroimidazole-‘4+1’ mixed ligand complexes in Swiss mice bearing fibrosarcoma tumor showed uptake and retention of the complexes in tumor.