Doxorubicin is a DNA-damaging drug, commonly used for treatment of cancer patients. Doxorubicin causes not only cytotoxic and cytostatic effects, but also inhibits metastasis formation, while TGFbeta1 (Transforming Growth Factor-beta1) is a cytokine that is often up-regulated in human cancers and can promote metastasis formation. We have studied the influence of Doxorubicin on TGFbeta signaling in tumor cells. Here we have demonstrated that Doxorubicin inhibited TGFbeta-signaling in human lung adenocarcinoma A549 cells, namely, it blocked TGFbeta1-induced activation of Smad3-responsive CAGA(12)-Luc reporter, but did not affect c-myc-Luc reporter. That effect was observed as early as after 1-3 h of treating these cells with Doxorubicin, while the other drugs cisplatin or methotrexate did not alter activation of CAGA(12)-Luc reporter under the same conditions. Besides, after 1 h action, Doxorubicin abrogated TGFbeta-induced translocation of Smad3-protein from the cytoplasm to the nucleus. Down-regulation of expression of Smad2, Smad3, and Smad4 proteins, and up-regulation of inhibitory Smad7 protein upon Doxorubicin treatment, were found after 12-24 h of Doxorubicin treatment. Phosphorylation of Smad2/3 proteins was also affected by Doxorubicin. Summarizing, we have found that human tumor cells treatment with Doxorubicin resulted in the inhibition of TGFbeta-signaling at both early (1 h) and later (12 h) stages of the drug action. Such inhibition can be a new potential mechanism for Doxorubicin action towards tumor cells.