An earphone sensor system for measuring electrocardiogram signals provides convenient and comfortable noninvasive electrocardiogram signal measuring for a subject. The electrocardiogram signal measuring system includes an electrocardiogram signal analyzing apparatus and an earphone sensing apparatus. The electrocardiogram signal analyzing apparatus includes an amplifier module, a microcontroller, a display, a radio module and a housing having conductive contacts. The earphone sensing apparatus includes an earphone and an electrode. The electrode is disposed in the earphone, and can be electrically connected to the subject for collecting the weak electrocardiogram signal at the head of the subject. By contacting the body surface of the testee with the housing having conductive contacts and the electrode, a basic loop for collecting the electrocardiogram signals is formed. The earphone sensor system can be associated with commercial gadgets and used for musical treatments and bio-feedback.