Problem: To provide a novel copolymer capable of use as a surface treatment agent which is safe and does not generate hydrogen, which has good compatibility with other cosmetic raw materials so as to be able to improve compounding stability of a cosmetic, which contributes to good water resistance, sebum resistance, gloss, feel, hair attachment ability, skin attachment ability and the like of a cosmetic, which further may be used for treatment of powders of a wide range of cosmetics, and which nearly entirely suppresses the occurrence of dispersion failure on the skin.Resolution Means: A copolymer comprising: (A) an unsaturated monomer having a carbosiloxane dendrimer structure; and (B) an unsaturated monomer having at least one hydrophilic group in the molecule. A content of the unsaturated monomer having the carbosiloxane dendrimer structure is in the range of 35 to 50% by mass of the total monomer units of the copolymer. The present invention is also a liquid composition, surface treatment agent, and powder composition including such a copolymer, as well as a cosmetic raw material containing such components.