An optical fiber connector includes a casing body formed with upper and lower key slots, a polarity adjusting key detachably mounted in a selected one of the key slots and engaging an adaptor, head and tail sleeves disposed respectively on front and rear ends of the casing body, and two core heads disposed between the head sleeve and the casing body. To adjust the polarity of the optical fiber connector, the optical fiber connector is detached from the adaptor and the optical fiber connector is inverted. Then, the polarity adjusting key is operated to disengage from the selected one of the key slots and engage the other one of the key slots to adjust the polarity without removal of head and tail sleeves.