A printing system and printer with an electronic signature capability, and a method thereof are provided. To print security documents using an electronic signature stored in a portable memory, the printing system of the invention includes a portable memory for storing an electronic signature. A memory interface connects detachably to the portable memory. A printer receives the electronic signature from the memory interface, composes the received electronic signature with print data, and executes a print operation. Accordingly, a stamping or signature process on numerous documents can be facilitated, and excessive stamping or signature execution can be prevented. Moreover, the electronic signature of the invention can be executed on various types of forms or documents.