Compared to solid-state devices,conventional vacuum electron devices such as travelling-wave tubes,backward wave oscillators and klystrons are much bigger and heavier.In order to improve the output power and reduce the size,we discuss the feasibilities of using metamaterials which are artificial electromagnetic materials.In this talk,we first review an exotic physical phenomenon: reversed Cherenkov radiation in the metamaterials.Based on this physical mechanism,we develop a new research field: metamaterials-inspired vacuum electronics.metamaterials-inspired vacuum electron devices(MIVEDs)have some attractive advantages over the traditional vacuum electron devices(TVEDs)such as: miniaturization,an all-metal construction to avoid dielectric breakdown,an enhanced transmission due to resonant effects,and easier fabrication and assembly.Then we describe one example of a MIVED to demonstrate its advantages in details.MIVEDs operating from microwave to Terahertz bands are also addressed.Finally,we discuss the pending technical challenges of these new MIVEDs.