A method of preparing an adsorbent for removing siloxane, in which the method includes mixing a silica particle and an OH compound to bond OH functional groups to the silica particle; measuring percentage by weight of OH bonded to the silica particle; calculating a bonding number and spacing of the OH functional groups by the percentage by weight of OH bonded to the silica particle; performing an evaluation of an adsorption rate and desorption rate of the silica particle to which the OH functional groups, of which the bonding number and spacing are calculated, are bonded; and adjusting the bonding number of the OH functional groups in the silica particle according to the evaluation.