Knockdown frame (10) for chairs (15) provided with at least a seat part (13) and a backrest (14), comprising at least a first component (11), able to rest on the floor and support the seat part (13), and at least a second component (12) able to support the backrest (14), the second component (12) including, in a single piece, first means (26a and 40a) to associate with the first component (11) and second means (26b and 40b) to support and associate with the backrest (14), the first means (26a and 40a) cooperating with the first component (11) for a substantial segment of its depth and being constrained thereto at least in correspondence with its front half.