Parabens are a group of preservatives that have vast indications in pharmaceuticals, cosmetics and food industries. Recently, there have been reports about the estrogenic effects of these compounds which raised concerns about the possibility of involvement of parabens in estrogen-responsive cancers. In the current study, the effect of methylparaben (MP) and propylparaben (PP) was assessed on the growth pattern of human breast adenocarcinoma cell line, MCF-7. 17-ß-estradiol (EST) and tamoxifen (TAM) were used as estrogenic and anti-estrogenic compounds. EC50 of EST and IC50 of TAM were calculated to be 1.206 and 7.017 µg/ml, respectively, based on trypan blue dye exclusion assay in a 5-day exposure. Proliferation kinetics of MCF-7 cells in a 10 day exposure to these compounds showed that EST (1.206 µg/ml) could induce cell proliferation, while exposure of MP or PP (at the same dose) did not change the growth curve of MCF-7. TAM, on the other hand could decrease the proliferation rate of MCF-7. This inhibition was more exacerbated when MP and PP were added to the culture media, suggesting a competitive binding of these compounds to receptors. In conclusion, the data propose the probable estrogenic effect of MP and PP with less potency compared to EST and less competitive binding to ERs compared to TAM.