One-dimensional nanostructured materials are often used as beams in many applications such as ultrahigh-frequency resonators and ultrasensitive sensors.Compared with usual macroscopic beams,nanobeams have much higher surface/volume ratios so that their surface energies may play a significant role.Besides,they often bear large deflections due to their typically large slenderness ratios and larger elastic ranges.There is,however,lack of a theory that takes into account of both the above two features owned by nanobeams.In this paper,we present such a theory and give applied examples to show that surface energy and large deflection may individually or jointly have notable effects.