Colloidal semiconductor is of interest as photocatalyst for various pro-cesses.A particular attention has been given to the so-called Q-particles ofsemiconductor witn respect to a“quantum size effect”[1].Recently,we re-ported that 1 nm ZnS particles could be obtained by embedding them Into β-cyclodextrin( BCD) cavities[2]and the resulting ZnS/BCD inclusion complexshowed much higher efficiency in simultaneous photocatalytic production ofhydrogen and ethylene glycol from aqueous methanol solution[3].In thiswork,we briefly present experimental evidence for the size quantization ef-fect of such small ZnS particles on the photocatalysis. Colloidal semiconductor is of interest as photocatalyst for various pro-cesses. A particular attention has been given to the so-called Q-particles of semiconductor witn respect to a “quantum size effect” [1]. Recently, we re-ported that 1 nm ZnS particles could be obtained by embedding them Into β-cyclodextrin (BCD) cavities [2] and the resulting ZnS / BCD inclusion complex showed much higher efficiency in simultaneous photocatalytic production of hydrogen and ethylene glycol from aqueous methanol solution [3] .In thiswork, we briefly present experimental evidence for the size quantization ef-fect of such small ZnS particles on the photocatalysis.