In a mat fastener for preventing a mat disposed on a carpet provided on a vehicle body panel from moving, a first fixing member is fixed to the carpet. A second fixing member is fixed to the mat. An operational mounting member is arranged to mount the second fixing member to the first fixing member. The first fixing member includes a supporting portion arranged to support the operational mounting member, and an engaging portion arranged to hold the second fixing member. The second fixing member includes a locked portion arranged to be locked on the operational mounting member, and an engaged portion arranged to be engaged with the engaging portion in a state where the second fixing member is mounted to the first fixing member by the operational mounting member.