Disclosed is a tin-silver alloy electroplating bath containing: (A) stannous salt; (B) silver salt; (C) one kind or two or more kinds of acids selected from the group consisting of sulfuric acid, phosphoric acid, phosphonic acid, hydroxycarboxylic acid, alkanesulfonic acid, and alkanolsulfonic acid; (D) thiourea; (E) nonionic surface active agent; and (F) one kind or two or more kinds of additives selected from the group consisting of a mercapto group containing aromatic compound, dioxyaromatic compound, and unsaturated carboxylic acid. The electroplating using the above electroplating bath is allowed to form a homogeneous tin-silver alloy plated film having a good external appearance by eliminating preferential deposition of silver and substitutional deposition of silver on an anode and the plated film.