Objective: To explore whether lower concentrations of phthalates interfere with the effects of 17β-estradiol on the growth of MCF-7 breast cancer cells. Materials and Methods: MCF-7 cells were treated with 17β-estradiol (E2), phthalates, including butyl benzyl phthalate (BBP), di(n-butyl) phthalate (DBP), and di(20ethylhexyl) phthalate (DEHP), or with both E2 and phthalates, all at 10nM. After incubation for 48 hours, the cells were harvested and extracted for MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. The proteins involving proliferative and apoptotic pathway were then evaluated using Western blot analysis. Results: In MCF-7 cell cultures, the MTT assay revealed a significant increase in cell viability with E2 and these three phthalates, and significantly more cell proliferation with the combination of E2 and phthalates. Proliferating cell nuclear antigen, as well as phosphatidylinositide 3-kinase (PI3K) and p-Akt, were all substantially increased in cultures with E2, phthalates, and the two combined. An additive effect of phthalates on the obvious increase of Bcl-2 and ER α expression was also noted in the presence of E2. Conclusion: The present study demonstrates that even at a very low concentration, BBP, DBP, and DEHP were not only still capable of displaying estrogenic activity, but also of inducing an additive proliferative effect through the PI3K/Akt signaling pathway and preventing apoptosis in the presence of E2. Therefore, the effects of current reference doses for phthalates defined by the government, especially for premenopausal women, should be further considered.