A paper feeding mechanism applied to an office machine for feeding a paper is disclosed. The paper feeding mechanism comprises a first adjusting board having a first fixing component, a second adjusting board having a second fixing component, a paper feeding body having a first groove and a second groove wherein the first fixing component is penetrated through the first groove and the second fixing component is penetrated through the second groove, and a flexible component having a bending structure wherein one end of the flexible component is fixed on the first fixing component of the first adjusting board and the other end of the flexible component is fixed on the second fixing component of the second adjusting board. Thereby the first adjusting board and the second adjusting board are moved simultaneously and in opposite directions by means of the bending structure so as to adjust a relative distance between the first adjusting board and the second adjusting board in response to a size of the paper.