Vestibular compensation after unilateral labyrinthectomy (UL) in mice was investigated by measuring the gain of horizontal vestibulo-ocular reflex (HVOR) with an infrared system. Six C57BL/6 mice underwent unilateral labyrinthectomy by injection of ethanol into the semicircular canal. Before UL, HVOR gain under sinusoidal rotation with a maximal head velocity (HV max) of 40 deg/sec and a frequency range between 0.1 and 3.2 Hz was analyzed. Before and after UL, gain of HVOR under sinusoidal rotation with an HV max of 150 deg/sec and a frequency of 1.6 Hz was analyzed. After UL, HVOR gain decreased showing a minimal value of 21% of preoperative value on the second postoperative day, then recovered to 65% of the preoperative value by the 28th postoperative day. These results provide fundamental data as a reference for future studies on vestibular compensation in genetically-manipulated mice.