A modular unit for forming a box-like module (100, 101) for a piece of furniture, such as a modular kitchen, said modular unit comprising: a bottom panel, a right panel, and a left panel, made of a thin metal sheet and coupled to one another to define an open box-shaped inner cavity, each of said right panel and left panel comprising an inner panel face (20', 30'), facing the inner cavity, and an outer panel face (20"), not facing the inner cavity and extending mainly according to a first extension direction and a second extension direction perpendicular to the first extension direction and extending much less in a third extension direction perpendicular to the first and to the second extension directions, i.e. being of a small thickness in the third extension direction, wherein each of said right and left panels comprises at least one upper panel edge (21, 31) and a lower panel edge (22, 32) which delimit the extension of the panel along the first extension direction, wherein close to said upper edge (21, 31) and lower edge (22, 32), each panel comprises a fold (210, 220) of the metal sheet comprising a blocking wall (210', 220'; 310') extending along the first extension direction much less than the extension of the entire panel along the same first extension direction and being spaced apart from the outer panel face, fixing openings (211, 221) being obtained on said blocking wall (210', 220'; 310') for removably fixing a finishing element or an equal modular unit; characterized in that the bottom panel, the right panel, and the left panel are made in a single piece and obtained by folding a single metal sheet along weakenings (12', 13') of the metal sheet. a bottom panel, a right panel, and a left panel, made of a thin metal sheet and coupled to one another to define an open box-shaped inner cavity, each of said right panel and left panel comprising an inner panel face (20', 30'), facing the inner cavity, and an outer panel face (20"), not facing the inner cavity and extending mainly according to a first extension direction and a second extension direction perpendicular to the first extension direction and extending much less in a third extension direction perpendicular to the first and to the second extension directions, i.e. being of a small thickness in the third extension direction, wherein each of said right and left panels comprises at least one upper panel edge (21, 31) and a lower panel edge (22, 32) which delimit the extension of the panel along the first extension direction, wherein close to said upper edge (21, 31) and lower edge (22, 32), each panel comprises a fold (210, 220) of the metal sheet comprising a blocking wall (210', 220'; 310') extending along the first extension direction much less than the extension of the entire panel along the same first extension direction and being spaced apart from the outer panel face, fixing openings (211, 221) being obtained on said blocking wall (210', 220'; 310') for removably fixing a finishing element or an equal modular unit; characterized in that the bottom panel, the right panel, and the left panel are made in a single piece and obtained by folding a single metal sheet along weakenings (12', 13') of the metal sheet.