A　novel　process,　i.e.,　ultrasound-assisted　membrane　reduction,　was　introduced　and　applied　to　synthesize　Ag　and　Au　nanocrystals.　High-resolution　transmission　electronic　microscopy　and　UV-vis　spectra　were　adopted　to　observe　and　study　the　resulting　colloids.　The　nearly　spherical　Ag　and　Au　nanoparticles　with　mean　diameters　of　5.8　and　6.8　nm,　respectively,　were　synthesized　with　the　novel　method.　The　silver　nitrates/hydrogen　tetrachloroaurate　hydrate,　sodium　borohydride,　and　poly(N-vinyl-2-pyrrolidone)　(PVP)　were　used　as　metal　precursor,　reductant,　and　stabilizer,　respectively.　The　reverse　mixing　of　silver　nitrate　and　reductant　resulted　in　larger　Ag　nanoparticles　in　the　range　of　5-24　nm.　The　addition　of　ethylenediaminetetraacetic　acid　(EDTA),　which　may　serve　as　the　second　protecting　agent　together　with　PVP,　could　reduce　the　Au　particle　size　to　a　mean　value　of　2.6　nm.　By　varying　the　NaBH4　injection　rate　in　the　process,　a　portion　of　the　primary　An　crystallites　could　be　self-assembled　to　form　decahedral　Au　nanocrystals　with　a　diameter　of　ca.　24　nm.　The　two-dimensional　networked　gold　nanowires　with　mean　diameters　of　5-10　nm　could　be　fabricated　by　regulating　the　acidity　of　the　reaction　system　to　pH　10　with　aqueous　ammonia.