A foldable chair includes first and second leg frames intersecting each other, and having left and right legs respectively formed with brackets, a pivot rod having opposite ends extending oppositely through the brackets, two extension rods telescopically inserted into the left and right legs of the second leg frame, and a seat frame pivoted to top ends of the left and right legs of the first leg frame and top ends of the extension rods. Each of the legs of the second leg frame has a tongue member mounted thereon, which is movable between an engaging position, in which the tongue member engages a through-hole in a respective extension rod, and a disengaging position, in which the tongue member disengages from the through-hole.