Silver and nickel are mutually only very slightly soluble and have a positive heat of mixing. Ag50Ni50 powder was prepared by mechanical alloying (MA) for 200 h and subsequent hot pressing (HP) at 620°C under 60 MPa. XRD results indicated that ball milling produced a two-phase mixture of supersaturated, nanocrystalline Ag-rich (α-phase) and Ni-rich (β-phase) solid solutions with grain sizes of 5 and 4 nm, respectively. The grain sizes increased to about 40 and 26 nm after hot pressing. The HP Ag50Ni50 had a density very close to the theoretical value. The HP alloy consisted of an interconnected network of the α-phase and islands of a two-nanophase mixture rich in the β-phase. The stability of the microstructure of the alloy and the effects of mechanical alloying on the supersaturation of the two phases and on the formation of the Ag-rich network are also discussed.