Abstract: Provided are a smoothness improving additive for a calendering process and a polyvinylchloride-based composition including the same. More particularly, a smoothness improving additive allowing, even in the case of using a plasticizer in a smaller amount than the conventional amount used, excellent productivity and excellent processability in a calendering process to accelerate a production speed, excellent mechanical physical properties such as glass transition temperature and tensile strength of a molded body, and manufacture of a molded body having better smoothness is provided.