For the practical applications, electrospun nanofibers with proper mechanical properties are highly required. This chapter presents several approaches to achieve improved mechanical properties of electrospun fibers. Mechanical properties of electrospun nanofibers are usually affected by the deposited formations of nanofibers, such as random or aligned assembling electrospun nanofiber mats. However, both kinds of fibrous mat contain a high porosity, which significantly influence the intrinsic mechanical properties of electrospun fiber mats. Besides polyamic acids and polyimide single electrospun nanofiber, other polymer single electrospun nanofiber were also studied regarding their mechanical properties, such as nylon, polyacrylonitrile, polylactide, and poly(ε-caprolactone). In these reports, the mechanical properties are significantly increased when the fiber diameter decreased. This phenomenon was called size effect on mechanical properties of electrospun nanofibers. Mechanical properties of electrospun fibers could be improved by blending different polymer components with different mechanical properties. Blending different polymers in one electrospinning solution is a straightforward way to produce composite electrospun fibers with modified mechanical properties.