Abstract: The present disclosure provides a method for inducing transdifferentiation of somatic cells into mammary epithelial cells in vitro using a small molecule compound. The method includes: inhibiting an expression of TGFbeta R1 and related sites thereof, to induce the transdifferentiation of the somatic cells into the mammary epithelial cells in vitro. The present disclosure fills a gap in the technology of inducing the transdifferentiation of fibroblasts to the mammary epithelial cells using the small molecule compound; the present disclosure also provides a research platform for in vitro researches on a mammary gland bioreactor, mammary gland development and differentiation, breast cancer, and transdifferentiation of the fibroblasts into other types of functional cells.