Abstract： Objective To inhibit the expression of transcription factor special protein 1(Sp1) through RNA interference (RNAi) technique and to investigate its impact on the proliferation ability of colorectal cancer cell line SW620. Methods The recombinant plasmid of Sp1 RNAi (pGenesil-1-Sp1) was constructed and transfected into SW620 cells by Lipofectamine. The transfcction efficiency was observed under fluorescence confocal microscopy. Expression levels of Sp1 mRNA and protein from SW620 after transfection were examined by real time PCR and Western blot respectively, after transduction of the recombinant plasmid into the SW620. The proliferation ability of SW620 cell line was evaluated by MTT assay. Results The expression plasmid (pGenesil-1-Sp1) against Sp1 was successfully constructed, recombinant vectors could reduce the expressions of Sp1 mRNA and protein in SW620, the ratio of inhibition of the expression of Sp1 mRNA and protein was 68.47 % and 73.82 % in 48th hour respectively. Compared with the control group, the difference was significant (P <0.05). MTT showed that the proliferation ability of SW620 cell was degraded. Conclusion Silencing Sp1 gene by the RNAi technology can actively inhibit the proliferation of SW620 cell. The successful application of Spl SiRNA extends the list of available therapeutic modalitics in the treatment of human colon cancer.