Abstract: The direct labeling method of ⁹⁹Tc^m was applied to labeling monoclonal antibodies for CD44， and then the properties of the labeling antibodies were identified; as well as biodistribution concerning nude mice bearing lung adenocarcinoma was made by applying ⁹⁹Tc^m-CD44-McAb. The results indicated that the labeling yield of CD44-McAb with ⁹⁹Tc^m was 92.3 %±4.1 %, Specific activity of the labeled antibody was 2.9±0.5 TBq/g ， and the radiochemical purity was 96.2 %±3.1%. The tumor tissue had high uptake of the labeled antibodies. The T/NT measured through ROI technique were 2.29±0.56. The biodistribution results of the labeled antibodies and their imaging results were basically identical. The results showed that the ideal target to non-target ratios could be obtained by applying ⁹⁹ Tc^m-CD44-McAb to radioimmunoimaging of nude mice bearing lung adenocarcinoma, and CD44 may be one of ideal target antigen to lung adenocarcinoma for radioimmunoimaging.