A beryllium copper alloy is provided, having a thickness "t" in a range from 0.05 mm to 0.5 mm and having an alloy composition consisting by weight (or mass %), of Cu.sub.100-(a+b)Ni.sub.aBe.sub.b, wherein 1.0.ltoreq.a.ltoreq.2.0, 0.15.ltoreq.b.ltoreq.0.35, and 5.5 .ltoreq.a/b.ltoreq.6.5. The beryllium copper alloy also exhibits a 0.2% proof stress equal to or above 650 MPa, an electric conductivity equal to or above 70% IACS, and a bending formability defined by a ratio of R/t=0, wherein "R" is a maximum bend radius before cracking at a bent portion when the beryllium copper alloy is bent into a V shape at a right angle.