The present application relates to a method for preparing a base film, a laminate or a polarizing film. The present application can provide an elongatable base film which simultaneously maintains elongation and recovery rates at proper levels and guarantees water resistance, and thus can be effectively applied in the preparation of, for example, a polarizing film. The present application can also provide a laminate using the film or a method for preparing a polarizing film using the base film. The base film can be effectively applied in the preparation of a polarizing film having an excellent function, such as polarization performance, while having a thickness of, for example, about 10 μm or less, about 8 μm or less, about 7 μm or less, about 6 μm or less, or about 5 μm or less.