It had been proved by many evidences that several heat shock proteins (HSPs) expression is up-regulated in tissue-derived primary lung cancer, and HSPs may play important roles in development, in resistant to drugs and in prognosis of lung cancer. However, there have not still systemic research on which HSPs，especially HSP70 can be or not thought as a new biological target in the therapy to lung cancer. In order to address the expression and roles of heat shock protein 70 (HSP70) in lung adenocarcinoma, immunoblotting was performed to detect the expression of HSP70 in tissue specimens from lung adenocarcinoma which were diagnosed unambiguously by branch fibromicroscopy and were excised. It showed that in the normal lung tissues, the expression of HSP70 was less then that in cancer tissues. After down-regulation of HSP70 protein by HSP70 anti-sense oligonucleotides in A549 cell line, MTT assay showed that the proliferation of A549 cells was inhibited remarkably after the treatment with HSP70 antisense oligonucleotides and Act D. There had significant differential in HSP70 antisense treatment group followed by Act D treatment and Act D treatment group. Results of Hoechst33258 staining revealed that HSP70 antisense oligonucleotides could promote Act D-mediated apoptosis in A549 cells with a higher percentage of apoptotic cells (26.91±3.73)% than that of Act D-treated group (16.83±3.41)% (P < 0.01). Furthermore, the expression of HSP70 protein was increased remarkably by transfection with a full length HSP70 recombinant plasmid into A549 cells. MTT assay revealed that HSP70 over-expression could block significantly the inhibition of proliferation induced by Act D, there had statistic significance between HSP70 over-expression group and only Act D-treated group (P < 0.01). Furthermore, over-expression of HSP70 could significantly inhibit Act D-mediated apoptosis in A549 cells with a lower percentage of apoptotic cells (4.25±1.48)% in HSP70 transfection group, (12.89±2.03)% in vector transfection group and (14.37±2.56)% in Act D treatment group and disappearance of DNA laddering. These results suggests that increased levels of HSP70 in lung adenocarcinoma tissues decrease the sensitivity of lung adenocarcinoma to Act D, promote proliferation and suppress apoptosis of lung adenocarcinoma cells.