Abstract: A pen cap and a pen barrel coupling structure provides the pen cap formed in hollow to hold a magnet and an opening at one end and the pen barrel couplable with the opening of the pen cap and having a metal element attractable to the magnet. The pen cap and pen barrel have respectively a first coupling portion and a second coupling portion that correspond to and engageable with each other. The first and second coupling portions form a first coupling position to allow the magnet and metal element attracting to each other to form an anchor condition, and a second coupling position to separate the magnet and metal element to release the anchor condition. Thus by moving the pen cap against the pen barrel to the second coupling position, the pen cap can be separated from the pen barrel to make use of the pen easier.