Abstract: NHS-MAG 3 is synthesized. A 15-base single-stranded amine-derivitized antisense oligonucleotide(ASON) complementary to c-myc oncogene mRNA is coupled with NHS-MAG 3 and labeled with 99 Tc m. 99 Tc m-ASON is purified on a φ 0.5 cm×30 cm gel filtration column of Sephadex G25, then the stability is evaluated. The results show that the average labeling efficiency of 99 Tc m-ASON is 68.4%,the radiochemical purity remained higher than 94% for 4 h after labeling at room temperature. When incubated with fresh human serum, 99 Tc m-ASON is stable, no degeneration is observed and the serum protein binding of 99 Tc m-ASON is low. The biodistribution in tumor-bearing nude mice shows that the highest uptake of tumor is 6.22 %ID/g at 2 h. Using NHS-MAG 3 as an efficient chelator, ASON has been successfully labeled with 99 Tc m. 99 Tc m-ASON has desirable stability, higher uptake in tumor and may provide a new sensitive tool for diagnostic imaging and therapy of tumor in the future.