A novel metal-organic chemical vapor deposition(MOCVD) process with a mixed metal beta-diketone precursor to successfully prepare Pd and Pd-Ni alloy composite membranes is described. A palladium phase deposit consisting of agglomerates of tiny crystallites with a dimension of around 30 x 10 nm was formed on porous Al2O3 substrates, when using a single Pd(AcAc)(2) precursor. With a mixed precursor of Pd(AcAc)(2) + Ni(AcAc)(2), uniform and dense Pd-Ni alloy membranes (consisting of primary crystallites with a dimension of 40 x 15 nm) were reproducibly obtained on porous alumina supports. N-2 permeation tests indicated that the Pd-Ni alloy layer was gastight and crack-free. XPS studies revealed that no oxygen nor carbon impurities were incorporated into the bulk membranes. The Pd/Ni ratio on the surface of Pd-Ni alloy layer was very close to that of the mixed precursor, but much less Ni content (<1/150) was detected in the deposit body.