We report the concurrence of de-alloying and re-alloying in a ternary Al67Cu18Sn15 alloy (at.%) de-alloyed in a 5 wt.% hydrochloric acid (HCl) solution at 70 ± 2 oC, and the fabrication of three-dimensional (3D) nanoporous Cu3Sn-Cu-Cu6Sn5 composite in the existence form of self-supporting foils. Re-alloying occurred in Al67Cu18Sn15 compared to de-alloying alone in binary Al-Cu alloys. Both Cu3Sn and Cu6Sn5 phases formed through an accompanied re-alloying process. This finding further proves the temperature sensitivity of phase formation in the Cu-Sn system established from Cu-Sn diffusion couple studies, and demonstrates the capability of designing and creating nanoporous composite materials via de-alloying a multicomponent alloy.