A frame height adjusting mechanism is adapted for a frame including an inner pipe and an outer pipe sheathing on the inner pipe. A fixing hole is formed on one of the inner pipe and the outer pipe. A plurality of positioning holes is formed on the other one of the inner pipe and the outer pipe. The frame height adjusting mechanism includes a driving member which is slidably disposed on the inner pipe or the outer pipe where the fixing hole is formed and includes at least one first inclined surface, and at least one engaging member which is slidably disposed on the driving member and passing through the fixing hole to insert into one of the plurality of positioning holes. The at least one first inclined surface pushes the at least one engaging member to disengage from the corresponded positioning hole when the driving member slides upwardly.