We demonstrate that Cu2O particles can be produced along with siloxene formation by simply dispersing layered CaSi2 into an aqueous solution of CuCl2 and HCl at room temperature. The Cl- ions induce oxidative extraction of Ca from CaSi2 to form siloxene and trigger the reductive deposition of Cu particles. All particles are then gradually oxidized to form Cu2O particles under optimized conditions as follows. A trace amount of residual CaSi2 is dissolved in the solution, which provides OH- ions, and a portion of the formed Cu particles are dissolved as [Cu(OH)(4)](2-) ions. Accordingly, Cu2O particles would be formed through the comproportionation reaction between Cu and [Cu(OH)(4)](2-) ions in the solution. However, under conditions with an excess amount of Cl- ions results in further oxidation of Cu to also form Cu2Cl(OH)(3). Thus, CaSi2 acts as an effective reduction and/or oxidation mediator to tune the number of Cl- and OH- ions and control the oxidation state of Cu.