Abstract: Objective To explore the influence of extracellular pH（pHe） on the growth and biological behavior of tumor cells. Methods MTT assay, apoptosis assay and morphologic observation were applied to evaluate the growth of human colorectal cancer SW116 cells, LoVo cells and human gastric cancer MKN-28 cells at different pHe values. The expression of Bcl-2 and survivin genes were tested by real-time PCR. Results Compared with pHe7.4, the viabilities of all three cell lines were enhanced at pHe 6.8 (P<0.05). Morphological observation and apoptosis assay confirmed that the viabilities of tumor cells at pHe6.8 were as same as those at pHe 7.4. At pHe 6.8, the expression of Bcl-2 was decreased significantly (P<0.05) while the expression of survivin didn't show a significant change. Conclusion The low extracellular pH value induces the growth of tumor cells without viability or morphology change. Meanwhile, the expression of apoptosisrelated gene, Bcl-2 is affected.