Disclosed are an additive for cement compositions that includes a polycarboxylic copolymer and a cement composition including the same and, more particularly, an additive for cement compositions that includes a polycarboxylic copolymer and/or a salt thereof, wherein the polycarboxylic copolymer is a copolymer of a monomer mixture including an alkoxy polyalkylene glycol mono(meth)acrylic acid ester-based monomer, a (meth)acrylic acid-based monomer, a (meth)acrylic acid ester-based monomer, and a polyoxyalkylene alkenyl ether sulfate salt and a cement composition including the same.