A lead-free solder characterized as comprising 0.1 to 2 wt % of Cu, 0.002 to 1 wt % of Ni with the residue being Sn. The solder preferably contains Cu in an amount of 0.3 to 0.7 wt %, and more preferably it contains Cu in an amount of 0.3 to 0.7 wt % and Ni in an amount of 0.04 to 0.1 wt %. The solder can be prepared by adding Ni to a molten mother alloy of Sn--Cu, or by adding Cu to a molten mother alloy of Sn--Ni. A lead-free solder which further comprises 0.001 to 1 wt % of Ga is also disclosed. The lead-free solder can form a solder joint having a high strength and stability comparable to those of a conventional Sn--Pb eutectic solder.