A device for preparing adipose tissue for transplantation from lobular fat extracted, for instance by liposuction, said fat consisting of a fluid component comprising an oily component, a blood component and/or sterile solutions and a solid component comprising cell fragments, cells and one or more cell macroagglomerates of heterogeneous size, wherein said device comprising; - at least one washing and separating container having a washing chamber for washing the liposuctioned material, which 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 said material, particularly the fluid component, to exit said chamber through the outlet, said washing chamber including means for forming an emulsion of fluid components, by mechanical stirring; - size reducing means, provided in the washing and separating container or in a size reducing container having an inlet and an outlet which is adapted to be fluid-tightly connected to said washing and separating container, wherein said size reducing means are provided for reducing the size of the solid component of the lipoaspirate to averagely equal smaller cell agglomerates, having a size equal to or smaller than a given value, which means consist of at least one series of parallel or intersecting sheets or cutting wires, to form at least one size reducing net (3, 4), through which the liposuctioned material is passed, characterized in that said size reducing means comprise, alternatively: a first size reduction net, through which the liposuctioned material is forced before entering the washing chamber of the washing and separating container and a second size reducing net, having narrower meshes than the first size reducing net, through which the liposuctioned material is forced before the exit of the material for transplantation from the washing and separating container, or two reducing containers, which are adapted to be alternately connected by their outlets or inlets to the inlet or outlet of the washing and separating container, each provided with a size reducing net having different sizes in terms of the meshes for the cell agglomerates that form the solid component of fat located in an intermediate position between the inlet and the outlet of the reducing container, the downstream compartment of which, with reference to the direction of injection of fat, acting as a collection chamber for the reduced material, said compartment having a predetermined volume. - at least one washing and separating container having a washing chamber for washing the liposuctioned material, which 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 said material, particularly the fluid component, to exit said chamber through the outlet, said washing chamber including means for forming an emulsion of fluid components, by mechanical stirring; - size reducing means, provided in the washing and separating container or in a size reducing container having an inlet and an outlet which is adapted to be fluid-tightly connected to said washing and separating container, wherein said size reducing means are provided for reducing the size of the solid component of the lipoaspirate to averagely equal smaller cell agglomerates, having a size equal to or smaller than a given value, which means consist of at least one series of parallel or intersecting sheets or cutting wires, to form at least one size reducing net (3, 4), through which the liposuctioned material is passed, characterized in that said size reducing means comprise, alternatively: a first size reduction net, through which the liposuctioned material is forced before entering the washing chamber of the washing and separating container and a second size reducing net, having narrower meshes than the first size reducing net, through which the liposuctioned material is forced before the exit of the material for transplantation from the washing and separating container, or two reducing containers, which are adapted to be alternately connected by their outlets or inlets to the inlet or outlet of the washing and separating container, each provided with a size reducing net having different sizes in terms of the meshes for the cell agglomerates that form the solid component of fat located in an intermediate position between the inlet and the outlet of the reducing container, the downstream compartment of which, with reference to the direction of injection of fat, acting as a collection chamber for the reduced material, said compartment having a predetermined volume. a first size reduction net, through which the liposuctioned material is forced before entering the washing chamber of the washing and separating container and a second size reducing net, having narrower meshes than the first size reducing net, through which the liposuctioned material is forced before the exit of the material for transplantation from the washing and separating container, or two reducing containers, which are adapted to be alternately connected by their outlets or inlets to the inlet or outlet of the washing and separating container, each provided with a size reducing net having different sizes in terms of the meshes for the cell agglomerates that form the solid component of fat located in an intermediate position between the inlet and the outlet of the reducing container, the downstream compartment of which, with reference to the direction of injection of fat, acting as a collection chamber for the reduced material, said compartment having a predetermined volume.