To provide a thin paper having a uniform formation that can especially suitably be used for a heat-sensitive stencil printing base paper, or for a paper for a battery separator or for a capacitor.

The thin paper having a basis weight of 1-50 g/m2 is provided by using staple fibers (preferably drawn fibers and undrawn fibers) that are composed of a fiber forming thermoplastic polymer and has a fiber diameter D of 100-2000 nm and a ratio L/D of fiber length L to the fiber diameter D within the range of 500-2500, in an amount of 80 weight% or more based on the total weight of the thin paper.