A cutter holder has a holder body and a sleeve. The holder body has a first end, a middle, an insert part and a mounting part. The insert part is formed on the first end. The mounting part is formed on the middle of the holder body and has an outer thread formed around the mounting part. The sleeve is mounted around the mounting part and has an inner thread, multiple screw holes and multiple setscrews. The inner thread is formed on an inner surface of the sleeve, is screwed with the outer thread of the mounting part. The screw holes are separately defined through the sleeve. The setscrews are mounted in the screw holes and abut the mounting part.