Objective To investigate whether specific cellular uptake of 99Tcm-survivin-ASODN in nude mice bearing human HCC is influenced by its cytosine content. Methods Three kinds(A1, A2, A3)of synthesized survivin ASODN with three cytosine contents(10%, 20%, 30%), 20 bases per single-strand were prepared. They were labeled with 99Tcm by conjugating with a bifunctional chelator HYNIC, purified through Cellufine GH-25 and then encapsulated with liposome. Antisense gene imaging and the biodistribution of 99Tcm-HYNIC-survivin ASODN in nude mice bearing HCC were performed. The data were analysed by Kruskal-Wallis H test. Results At 4 h post injection, all the 3 labelled compounds showed increased uptake by tumor, liver and kidney. With increase in cytosine content, the uptake increased in kidney (%ID/g: 1.50±0.06, 2.80±0.09 and 3.96±0.03), and decreased in tumor (%ID/g: 2.08±0.08, 1.69±0.01 and 1.20±0.09). T/NT in imaging (4.49-4.93, 4.12-4.21, 3.35-3.85; H=12.50, P<0.05) and in biodistribution (4.08-4.94, 4.02-4.18, 3.66-3.85; H=10.82, P<0.05) were all significantly different. Conclusion ASODN with lower cytosine content shows higher uptake by HCC tumor cells and less stasis in kidneys, thus providing better quality in antisense gene imaging. Key words: Liver neoplasms; Cytosine; Oligodeoxyribonucleotides, antisense; Technetium; Tomography, emission-computed, single-photon; Mice, nude