Transforming growth factor beta (TGF-beta) is over-expressed in a wide variety of cancer types including lung adenocarcinoma (LAC), and the TGF-beta signaling pathway plays an important role in tumor development. To determine whether blockade of the TGF-beta signaling pathway can inhibit the malignant biological behavior of LAC, RNA interference (RNAi) technology was used to silence the expression of TGF-beta receptor, type II (TGF beta RII) in the LAC cell line, A549, and its effects on cell proliferation, invasion and metastasis were examined. Three specific small interfering RNAs (siRNAs) designed for targeting human TGF beta RII were transfected into A549 cells. The expression of TGF beta RII was detected by Western blot analysis. Cell proliferation was measured by MTT and clonogenic assays. Cell apoptosis was assessed by flow cytometry. The invasion and metastasis of A549 cells were investigated using the wound healing and Matrigel invasion assays. The expression of PI3K, phosphorylated Smad2, Smad4, Akt, Erk1/2, P38 and MMPs was detected by Western blot analysis. The TGF beta RII siRNA significantly reduced the expression of TGF beta RII in A549 cells. The knockdown of TGF beta RII in A549 cells resulted in the suppression of cell proliferation, invasion and metastasis and induced cell apoptosis. In addition to the Smad-dependent pathway, independent pathways including the Erk MAPK, PI3K/Akt and p38 MAPK pathways, as well as the expression of MMPs and VEGF, were inhibited. In conclusion, TGF-beta signaling is required for LAC progression. Therefore, the blockade of this signaling pathway by the down-regulation of TGF beta RII using SiRNA may provide a potential gene therapy for LAC.