Abstract: ⁹⁹Tc^m Mannosylated dextran conjugates were prepared through ⁹⁹Tc^m(CO)₃⁺ precursor synthesized by carbonyl Isolink kit. The labelled conjugates were injected sub-dermally into the rear foots of the mice, and the patent blue solution was injected at the same site 10 min before sacrifice. The mice were killed at 1 h and 4 h postinjection, and the samples of different tissues including SLN, 2LN, injection site, liver, spleen, blood were dissected and counted. The uptake in terms was calculated. The results of biodistribution demonstrated that the SLN uptakes of radiopharmaceutical (without mannose in the molecules) were rather low and in vivo excretion of these conjugates were comparatively faster, and the uptake of injection site was also low; on the other hand, the SLN uptakes of radiopharmaceutical (with mannose in their molecules) were much higher than those of their corresponding dextran conjugates without mannose, but the retention in the injection site of these conjugates increased too. The results indicated that the affinity of mannosyl-dextran conjugates to the receptors on the surface of macrophages in the lymph node. In addition, the different relative molecular mass of dextran conjugates also cause different biodistribution results, the major one had higher SLN uptake, the difference was significant(P<0.005); moreover, the injected dosage of the labelled conjugates also had an affect on SLN uptakes. The ⁹⁹Tc^m(CO)₃⁺ labelled mannosylated dextran conjugates showed promising properties as SLN imaging agent and worth further investigation.