A rotary cutter assembly for a lighter comprises a lighter body which is defined with a receiving groove in an outer periphery thereof. A rotary plate is pivoted to the receiving groove in such a manner that the rotary plate can be rotated within the receiving groove. In the receiving groove is disposed a push pole, and on the rotary plate is provided an annular cutter. When the rotary plate is closed, the push pole is inserted in the annular cutter.