A dust proof structure for a machine tool includes a flow guiding element located therein. The machine tool includes a housing chamber to hold a spindle and the flow guiding element. The housing chamber has an air intake section and an air discharge section communicating with the air intake section. The machine tool further has an air inlet communicating with the air intake section and an air outlet communicating with the air discharge section. The spindle is coupled with an action member outside the air outlet. When the spindle drives the action member to operate, the flow guiding element introduces external air through the air inlet to the air intake section, and directs the air to the air discharge section to be discharged towards the action member. Hence dust generated by the action member during operation of the machine tool does not enter the machine tool through the air outlet.