Provided are a base film, a laminate, and a method of forming a polarizing film. Particularly, a base film which may effectively form a polarizing film having a thickness of approximately 10, 8, 7, 6, or 5 μm or less and exhibiting excellent functions such as polarizing performance, a laminate, and a method of forming the same are provided. Therefore, a polarizing film may be formed by preventing tearing or curling during an elongation process, and easily elongating a polarizing material such as a polyvinylalcohol-based resin.