A method for producing a mesenchymal cell line derived from a vertebrate adipose tissue, and a mesenchymal cell line derived from a vertebrate adipose tissue produced by the method. Advantageously, a method for producing a mesenchymal cell line derived from a vertebrate adipose tissue is achieved more simply, in a shorter period of time, and more efficiently. Also, a mesenchymal cell line is derived from a vertebrate adipose tissue produced by the production method. The method for producing a mesenchymal cell line derived from a vertebrate adipose tissue comprises: (A) inducing differentiation of one or more cells selected from a stromal vascular fraction comprising a mesenchymal stem cell, an adipose progenitor cell, and a stromal cell of a vertebrate adipose tissue into a mature adipocyte; and (B) inducing dedifferentiation of the mature adipocyte obtained in step (A) to obtain a mesenchymal cell line derived from the vertebrate adipose tissue.