A knowledge of the elastic properties of Cu and Ag-based intermetallics, formed during reflow of Sn-rich solder joints on Cu, is extremely important in understanding and predicting the mechanical behavior of the joint. Bulk testing of these intermetallics is problematic because of the difficulty in achieving fully-dense materials, and because the microstructure in bulk form is often quite different from that observed in the joint. In this study, we have used nanoindentation to probe the mechanical properties of intermetallics in the joint in situ. The Continuous Stiffness Method (CSM) was used during indentation to obtain the instantaneous Young’s modulus as a function of depth. The Young’s moduli of Cu6Sn5, Cu3Sn, Ag3Sn, Sn-Ag solder, pure Sn, and Cu, were measured by nanoindentation. After indentation, the surface characteristics of each phase were examined using atomic force microscopy (AFM). Significant dislocation pile-up was observed in Sn, Sn-Ag solder, and Cu. Finite element analysis was conducted to investigate and predict the deformation behavior during indentation and correlated very well with the experimental results.