The anti CD20 antibody Rituximab was conjugated with para iso thiocyanato benzyl diethylene triamine penta acetic acid (p-NCS-Bz-DTPA) and subsequent radio labeling with 99mTc was carried out via the ^99mTc carbonyl synthon. The ^99mTc labeled antibody conjugate exhibited >95% radio chemical purity After purification and retained good in vitro stability when studied upto 24 h at room temperature. In vitro cell binding studies carried out in Raji cells expressing CD20 antigen validated the biological efficacy of  the preparation.