A device and a method for preparing adipose tissue for transplantation from lobular fat material extracted by liposuction, the fat material consisting of a mixture of fluid materials and cell fragments, cells and one or more cell magroagglomerates of heterogeneous sizes, include at least one sterile container having a size reducing device for reducing the fat material into cell agglomerates of smaller and identical or similar sizes, the device dividing the inner chamber of the container into at least two portions, particularly a first upper portion and a second lower portion.
