A method for producing a lactase-containing composition which is purified by selectively removing protease contaminating the lactase using simple and easy means; a lactase-containing composition; and a dairy product containing the lactase-containing composition.A method for producing a lactase-containing composition having a reduced protease content includes: dissolving a composition containing lactase and protease in an aqueous salt solution having an electric conductivity of from 2 to 45 mS/cm; bringing the resultant solution into contact with an ion exchange resin; and collecting a fraction which is not adsorbed onto the ion exchange resin.