Experimental 30Pd-15Cu-54Ag and 12Au-20Pd-15Cu-52Ag alloys containing 1% zinc as a deoxidizer(APZ and APGZ)were prepared and a minimal mass of iridium, ruthenium and osmium determined by preliminary investigation, was independently inoculated into APZ and APGZ alloys.Using dental precision casting technique, cast specimens were made from these alloys and both mechanical properties and grain size of the the alloys were measured.Most of the mechanical properties of APGZ series were improved by inoculation with 200ppm Ir, 300ppm Ru and 200ppm Os.After softening heat treatment, tensile strength and elongation had a highly significant correlation with grain size, and significantly increased as the grain size decreased.