The ability to maintain and study human tissues in in-vivo environment has proved to be a valuable tool in breast cancer research for several decades. The most widely tissues have been xenografts established human breast cancer cell lines into athymic nude mice. The aim of this study was to provide a new accurate and affordable method for the establishment of breast cancer xenograftin nude mice. Injectable estradiol valerate was assayed as a substitute for estradiol pellets that are rather expensive in order to create cancer tumors by MCF7 xenograft method in nude mice (B6). Twenty four healthy adult female nude mice (B6) were injected with different concentrations of pre-counted MCF7 cells. Then estradiol valerate and Matrigel B.D. were injected either alone or combined in two different groups of animals. In a period of 6 to 9 weeks, mice injected with increased amount of MCF7 cells, estradiol valerate and Matrigel (combined or alone) developed faster and larger tumors than animals which received MCF7 only or MCF7 and Matrigel combined. The results indicate that estradiol valerate which is way less expensive than estradiol pellets can be used as tumor proliferator to create animal breast cancer models.