The high scattering cross-section for electron/matter interaction, the atomic-scale spatial resolution, and the ultrafast temporal resolution of ultrafast electron diffraction (UED) represent the key elements that make this technique a unique tool for the dynamic investigation of nanomaterials. This talk introduces the general concept of UED, and then presents a few applications on investigating the light-induced lattice deformation in solids, including transient structures of phase change materials, energy localization in quantum dots, and rippling dynamics of free-standing graphene.