A folding door (10) with a door lock is provided, comprising first and second walls (20, 177) pivotably connected together. The first panel (20) includes a chamber (32) and a mounting hole (34) intersecting with the chamber (32). A follower (46) is slideably mounted in the chamber (32) and includes a rack (58) in the mounting hole (34). First and second outer covers (70, 137) are mounted to first and second walls (26, 28) of the first panel (20). A driving member (96) is rotabably mounted between the first and second panels (20, 177) and meshes with a rack (58). The folding door (10) enhances structural strength and reduces manufacturing costs.