Different from the known setting and hardening properties of cementitious materials,this study focuses on the contact-hardening properties of nano- amorphous calcium silicate hydrate （C-S-H）. Two different types of C-S-H powders were used. The powders were compressed under 20~60 MPa for three minutes to produce compacts. Bulk density and compressive strength of the compacts as well as the microstructure of C-S-H before and after compaction were measured.The results show that nano C-S-H presents excellent contact-hardening cementitious properties. Lightweight and high strength compact can be produced by compression in several minutes. When the bulk density of the compact is about 800 kg/m3,compressive strength can be up to 20.0～30.5 MPa. According to the microstructure analysis,the distance of C-S-H particles is reduced during compaction because of the viscoelastic flow. Therefore,the particles become contact to each other,and attractive force between particles is formed. Furthermore,fragmentation and plastic deformation attributes to the compression pressure,leading to the formation of cohesion and adhesion structure. Consequently,the compressive strength of the compacts is greatly improved.