A portable stamp has a stamp box, an ink part and a stamping part. The stamp box has a first case and a second case pivotally connected to the first case. The ink part and the stamping part are mounted in the first case and the second case respectively. The first case has a peripheral wall and a positioning hole formed through the peripheral wall. The ink part is mounted in the peripheral wall and has a positioning plate mounted through the positioning hole. The ink part is located in the first case by the positioning plate. When replacing a dry ink part with a new one, a user just presses the positioning plate to loosen the dry ink part from the first case. Then the user can remove the dry ink part easily and mount the new ink part in the first case.