Abstract: An inflatable electroencephalogram measuring device comprises an inflatable helmet applicable for an user's head and at least one measuring electrode. A plurality of supporting strips are disposed within the inflatable helmet and the at least one measuring electrode is well distributed upon the supporting strips. When the inflatable helmet is inflated, the measuring electrode accordingly moves to make contact with the use's head so as to measure an electroencephalogram signal. By designing the inflatable electroencephalogram measuring device with an inflatable helmet, the proposed invention is widely utilized for measuring various users with a variety of head sizes, and thus is characterized with a potential for becoming an important tool of medical measurement.