Objective: To construct the small interfering RNA(siRNA) expression cassettes (SECs) targeting activated K-ras gene sequence and investigate the effects of SECs on K-ras gene in human pancreatic cancer cell line MIAPaCa-2. Methods: Three different sites of SECs were constructed by PCR. The K1/siRNA, K2/siRNA and K3/siRNA were located at the site 194, 491 and 327, respectively. They were transfected into MiaPaCa-2 cells by liposome to inhibit the expression of activated K-ras. In the interfering groups of site 194,491, we observed the cytopathic effect of confluent MiaPaCa-2 cells after they were incubated for 48 hours, and detected the apoptosis in cells by FACS, then we tested the altation of K-ras gene in confluent MiaPaCa-2 cells by RT-PCR,immunofluorescence and west blot, respectively. Results: Introductions of the K1/siRNA and K2/siRNA against K-ras into MiaPaCa-2 cells led to cytopathic effect, slower proliferation and increased apoptosis, while the appearances of control MiaPaCa-2 cells remained well. The number of apoptotic cells increased compared with control cells. RT-PCR,immunofluorescence and west blot showed the effects of inhibited expression of activated K-ras gene by RNA interference in the K1/siRNA and K2/siRNA groups. We also found that the introduction of K3/siRNA had no effect on MiaPaCa-2 cells. Conclusion: K1/siRNA and K2/siRNA can inhibit the expression of activated K-ras and decrease the growth of MiaPaCa-2 cells, while K3/siRNA has no such effect, demonstrating that the suppression of tumor growth by siRNA is sequence-specific. We conclude that K-ras is involved in maintenance of tumor growth of human pancreatic cancer, and SECs against K-ras expression may be a powerful tool to be used therapeutically against human pancreatic cancer.