An optical member driving mechanism for driving an optical member having an optical axis is provided, including a fixed portion, a movable portion, a driving assembly, and a circuit board. The fixed portion includes a case and a frame, and a gap is formed therebetween. The movable portion is movably connected to the fixed portion, and configured to hold the optical member. The driving assembly can drive the movable portion to move relative to the fixed portion. The circuit board is disposed in the gap, and has a plate portion and a protruding portion. The protruding portion is disposed between the plate portion and the fixed portion, so as to tightly dispose the circuit board in the gap.