A puzzle pen of which the penholder is formed of a shaft holding a writing member for writing, puzzle rings mounted on the shaft each holding a plurality of axially slidable puzzle blocks, and a retaining device, which has a locating ring with a receiving groove for receiving one puzzle block from the puzzle rings for enabling the user to rearrange the combination of the puzzle blocks, a cover shell rotatably mounted on the shaft to close/open the receiving groove of the locating ring, and a spring member supported between the locating ring and the cover shell to force the locating ring against the puzzle rings.