The effective adsorption capacity of hexamethycyclotrisiloxane (HMCTS), a common siloxane impurity in biogases, by solids, such as activated carbons (ACs), silica, and zeolite, has been evaluated in laboratory experiments using synthetic biogas. The adsorption mode of this molecule has been investigated by infrared (IR) spectroscopy. Similar experiments have been performed with exhausted ACs taken from a commercial adsorption column treating real landfill biogas. It has been found that pure ACs are efficient sorbents for HMCTS, better than alkali-impregnated ACs and inorganic solids. It was found that HMCTS converts in part upon adsorption into silicone and silica. This is likely a reason of the only partial regenerability of ACs after use in purification of real biogases.