Thin Pd and Pd-Ni alloy membranes were prepared by the MOCVD method using an cold-wall technique. Pd(C3H5)(C5H5) and Ni(C3H5)(C5H5) were decomposed into densely aggregated metal crystallites that were to plug mesoporous nickel-stainless steel (Ni-SUS) or gamma-Al2O3/alpha-Al2O3 supports. The use of highly volatile organometallic precursors enabled continuous and controlled deposition mode, which resulted in reproducible formation of thin impervious Pd or Pd-Ni alloy membranes. Pd(C3H5)(C5H5) and Nb(C3H5)(C5H5)(5) were deposited in a layer by layer deposition method. The H-2 permeance of the Pd/Ni-SUS membrane was 2.0-5.0x10(-2) cm(3) cm(-2) cmHg(-1) s(-1) (723 K); the H-2/N-2 selectivity was 1600. The H-2 permeance of the Pd/Al2O3 was 1.5x10(-2) cm(3) cm(-2) cmHg(-1) s(-1) (723 K); the H-2/N-2 selectivity was > 1000.