MgB2 superconductors can be synthesized through a new route by using Mg2Cu instead of pure Mg. When the heating temperature was raised to around the melting point (568 °C) of Mg2Cu, the Tc of PIT-processed Mg2Cu /B Fe-sheathed wires rapidly increased and reached about 37.5 K. Mg2Cu, with its low melting point, promoted the diffusion reaction to form the high Tc MgB2 at low temperatures. Many second phases of large size (several tens of micrometres) were formed with a small amount of MgB2 in the core of Mg2Cu /B Fe-sheathed wires. However, its transport Jc showed a rather high value, which was over 105 A cm-2 at 4.2 K in ambient fields. The Jc estimated from a net cross-sectional area of MgB2 must be very high. In addition, an Mg2Cu /plasma-splayed B/metal-substrate layered composite was also prepared in this study. After heat treatment at 600 °C for 10 h in vacuum, a 50 µm thick MgB2 diffusion layer was formed with a high density microstructure. Cu was released from Mg2Cu, forced out and gathered on the surface of the diffusion layer. This behaviour is similar to that of the bronze process used for Nb3Sn practical conductors.