A swingable exercise bicycle mechanism includes a base frame, two fastening seats at the front and rear, two extension springs arranged symmetrically in pairs connecting with the fastening seats, at least one sliding shaft extending between and being supported by the two fastening seats, a slider arranged on the sliding shaft, and a buffer arranged between each of the two fastening seats and the slider. An exercise bicycle is secured onto the top surface of slider. When a user swings their body on the exercise bicycle, the slider causes the fastening seats to rotate, and simultaneously generate a torque in the opposite direction, which enhances the swinging effect of the exercise bicycle. By moving the user's body back and forth, the exercise bicycle applies reciprocating component forces, which causes shifting of the slider, whereby damping by the buffer device is overcome to achieve the effect of intense exercise.