A turnbuckle is made by a method including preparing an iron tube having a longitudinal through-hole. A diameter of each of two ends of the iron tube is reduced to form a coupling section having an engaging hole, with an interconnecting section interconnected between the coupling sections. The interconnecting section is punched in a direction perpendicular to the longitudinal through-hole to form a transverse through-hole perpendicular to the longitudinal through-hole and between the coupling sections, leaving two opposite peripheral wall portions spaced by the transverse through-hole and forming a bend extending inward from each of two end edges of each peripheral wall portion into the longitudinal through-hole. An abutting portion is formed between each bend and one of the end edges of one of the peripheral wall portions. Inner threading is formed in the engaging hole of each coupling section.