Winter Butterfly is based on a true story.
Park So-yeon was on a diet for the movie, and tried to eat as little as possible to empathize with the character.
The initial title of the movie was "A Mother and a Son. But Kim changed his mind as he was finishing up editing the film because Director Kim Gyoo-min questioned whether a butterfly born in winter time would be happy. In the similar context, he wondered what could've been different if the mother and the son were born in South Korea. So he named the movie "Winter Butterfly"
Kim Gyoo-min decided to let his actors perform in their standard South Korean accent to allow them to act freely with raw emotion.