An adjustable supporting device for a display panel includes: a coupling seat connected pivotally to a supporting seat mounted on a supporting surface; a mounting frame coupled to the display panel and connected pivotally to the coupling seat; a torsion spring having a first end engaging the mounting frame, and a second end opposite to the first end and engaging movably the coupling seat, and operable to provide a torsional force for supporting an assembly of the mounting frame and the display panel at a desired orientation relative to the coupling seat; and an adjusting member disposed movably in the coupling seat, abutting against the second end of the torsion spring, and operable so as to adjust the torsional force provided by the torsion spring.