A padding structure for a chair includes a back support, a seat plate, a foam disposed on the back support, two guiding lines mounted on the back support, and two guiding lines mounted on the seat plate. Each guiding line of the back support and the seat plate is connected with a resilient member to control flexibility of the resilient member. An adjustable member is used to control the expansion and retraction of the guiding lines to drive the resilient members to change their radii of curvature, correcting the user's improper posture.