We observed the tensile deformation process of silver nanocontacts (Ag NCs) in situ at room temperature by high-resolution transmission electron microscopy. Simultaneously, the conductance and the tensile force of the NCs were measured. Stress-strain relationship of Ag NC was investigated. Typical saw-tooth curves showing elastic and plastic deformations of NCs were observed. The Young's modulus of NCs was estimated from the stress-strain curve. [DOI: 10.1380/ejssnt.2009.621]