A side-viewing endoscope structure includes a front tubular section, an intermediate tubular section, a rear cap and an optical imaging unit. The front tubular section includes a tube, a reflector holder, and a reflector. The tube includes a main body and a coupling portion. The reflector holder is fitted in the main body of the tube and provided on one side of an outer wall surface thereof. The reflector is arranged on the reflector holder. A length of the intermediate tubular section has a reduced outer diameter to match the coupling portion. The rear cap has a rear wall provided with a cable hole. The optical imaging unit is located in the intermediate tubular section and the rear cap, and includes a flexible printed circuit board, a camera lens, a light source and a cable so as to transmit images.
