A device and a method for preparing adipose tissue for transplantation from lobular fat extracted, for instance by liposuction, the fat including a fluid component that have an oily component, a blood component and/or sterile solutions, and a solid component including cell fragments, cells and one or more cell macroagglomerates of heterogeneous size, wherein the device includes at least one washing and separating container having a washing chamber, the container has an inlet and an outlet for the liposuctioned material to enter the washing chamber through the inlet and for at least part of the material to exit the washing chamber through the outlet, the washing chamber including stirring means for forming an emulsion of fluid components.