An adjustable support structure for a panel computer includes: a cradle having a slide slot at a middle section, at least two fastening slots placed at a bottom surface of the slide slot, and at least two pairs of positioning holes separately corresponding to the fastening slots are placed on two side walls of the slide slot. The back end of the support prop is optionally pushed against one of the fastening slots in the cradle; therefore, the cradle, the back support and the support prop which form a triangularly linked structure. The elastic unit can be pressed to drive the two positioning tabs to leave the positioning holes, so that the support prop can slide along the parallel track until the back support is at a desired leaning angle.