Di (n-ethylhexyl) phthalate (DEHP) is thought to mimic estrogens in their action, and are called endocrine disrupting chemicals. DEHP is used in numerous consumer products, especially those made of flexible polyvinyl chloride and have been reported to be weakly estrogenic. In this study, DEHP were tested for estrogenic properties in vitro models and with microarray analysis. First, the E-screen assay was used to measure the proliferation of DEHP in MCF-7 cells, a human breast cancer cell line. DEHP induced an increase in MCF-7 cell proliferation at concentration of $10^{-4}M$. Second, we carried out a microarray analysis of MCF-7 cells treated with DEHP using human c-DNA microarray including 401 endocrine system related genes. Of the genes analyzed, 60 genes were identified showing significant changes in gene expression resulting from DEHP. Especially, 4 genes were repressed and 4 genes were induced by DEHP compared to $17{eta}-estradiol$. Among these genes, trefoil factor 3 (intestinal), breast cancer 1, early onset and CYP1B1 are involved in estrogen metabolism and regulation. Therefore it suggests that these genes may be associated with estrogenic effect of the DEHP on transcriptional level. The rationale is that, as gene expression is a sensitive endpoint, alterations of these genes may act as useful biomarkers to define more precisely the nature and level of exposure to kinds of phthalates.