The use of hydrothermal methods has allowed the synthesis of a new silver copper mixed oxide, Ag2CuMnO4, the first example of a quaternary oxide containing both elements. It crystallizes with the delafossite 3R structure, thus being the first delafossite to contain both Ag and Cu. Synthesis conditions affect the final particle size (30–500 nm). Powder X-ray diffraction Rietveld refinement indicates a trigonal structure (R3¯m) and cell parameters a=2.99991Å and c=18.428Å, where Cu and Mn are disordered within the octahedral B positions in the plane and linearly coordinated Ag occupies de A position between layers. X-ray absorption near edge spectroscopy (XANES) for copper and manganese, and XPS for silver evidence +2, +4, and +1 oxidation states. The microstructure consists of layered particles that may form large twins showing 5 nm nanodomains. Finally, magnetic measurements reveal the existence of ferromagnetic coupling yielding in-plane moments that align antiferromagnetically at lower temperatures. The singularity of the new phase resides on the fact that is an example of a bidimensional arrangement of silver and copper in an oxide that also shows clear bidimensionality in its physical properties. That is of special relevance to the field of high Tc superconducting oxides, while the ferromagnetic coupling in a bidimensional system deserves itself special attention.